Fix clippy::needless_borrow warning

```
error: the borrowed expression implements the required traits
   --> src/lib.rs:212:57
    |
212 |                     signal_hook::iterator::Signals::new(&[signal_hook::consts::SIGCHLD])
    |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: change this to: `[signal_hook::consts::SIGCHLD]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
    = note: `-D clippy::needless-borrow` implied by `-D warnings`

error: the borrowed expression implements the required traits
  --> tests/std.rs:14:38
   |
14 |             Command::new("cmd").args(&["/C", "exit 0"]).spawn()
   |                                      ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 0"]`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
   = note: `-D clippy::needless-borrow` implied by `-D warnings`

error: the borrowed expression implements the required traits
  --> tests/std.rs:35:38
   |
35 |             Command::new("cmd").args(&["/C", "exit 1"]).spawn()
   |                                      ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 1"]`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
  --> tests/std.rs:87:22
   |
87 |             cmd.args(&["/C", "echo foobar"]).stdout(Stdio::piped());
   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "echo foobar"]`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:145:23
    |
145 |                 .args(&["/C", "exit 1"])
    |                       ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 1"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:156:23
    |
156 |                 .args(&["/C", "exit 0"])
    |                       ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 0"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:189:23
    |
189 |                 .args(&["/C", "echo hello"])
    |                       ^^^^^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "echo hello"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:213:23
    |
213 |                 .args(&["/C", "mkdir ."])
    |                       ^^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "mkdir ."]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:231:38
    |
231 |             Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
    |                                      ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 1"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:243:38
    |
243 |             Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
    |                                      ^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "exit 1"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

error: the borrowed expression implements the required traits
   --> tests/std.rs:257:23
    |
257 |                 .args(&["/C", "echo hello"])
    |                       ^^^^^^^^^^^^^^^^^^^^^ help: change this to: `["/C", "echo hello"]`
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
```

src/lib.rs

@@ -207,7 +207,7 @@ impl Child {
 
                 // Make sure the signal handler is registered before interacting with the process.
                 SIGNALS.get_or_init_blocking(|| Mutex::new(
-                    signal_hook::iterator::Signals::new(&[signal_hook::consts::SIGCHLD])
+                    signal_hook::iterator::Signals::new([signal_hook::consts::SIGCHLD])
                         .expect("cannot set signal handler for SIGCHLD"),
                 ));
 

tests/std.rs

@@ -11,7 +11,7 @@ use futures_lite::{future, prelude::*};
 fn smoke() {
     future::block_on(async {
         let p = if cfg!(target_os = "windows") {
-            Command::new("cmd").args(&["/C", "exit 0"]).spawn()
+            Command::new("cmd").args(["/C", "exit 0"]).spawn()
         } else {
             Command::new("true").spawn()
         };
@@ -32,7 +32,7 @@ fn smoke_failure() {
 fn exit_reported_right() {
     future::block_on(async {
         let p = if cfg!(target_os = "windows") {
-            Command::new("cmd").args(&["/C", "exit 1"]).spawn()
+            Command::new("cmd").args(["/C", "exit 1"]).spawn()
         } else {
             Command::new("false").spawn()
         };
@@ -84,7 +84,7 @@ fn stdout_works() {
     future::block_on(async {
         if cfg!(target_os = "windows") {
             let mut cmd = Command::new("cmd");
-            cmd.args(&["/C", "echo foobar"]).stdout(Stdio::piped());
+            cmd.args(["/C", "echo foobar"]).stdout(Stdio::piped());
             assert_eq!(run_output(cmd).await, "foobar\r\n");
         } else {
             let mut cmd = Command::new("echo");
@@ -142,7 +142,7 @@ fn test_process_status() {
     future::block_on(async {
         let mut status = if cfg!(target_os = "windows") {
             Command::new("cmd")
-                .args(&["/C", "exit 1"])
+                .args(["/C", "exit 1"])
                 .status()
                 .await
                 .unwrap()
@@ -153,7 +153,7 @@ fn test_process_status() {
 
         status = if cfg!(target_os = "windows") {
             Command::new("cmd")
-                .args(&["/C", "exit 0"])
+                .args(["/C", "exit 0"])
                 .status()
                 .await
                 .unwrap()
@@ -186,7 +186,7 @@ fn test_process_output_output() {
             stderr,
         } = if cfg!(target_os = "windows") {
             Command::new("cmd")
-                .args(&["/C", "echo hello"])
+                .args(["/C", "echo hello"])
                 .output()
                 .await
                 .unwrap()
@@ -210,7 +210,7 @@ fn test_process_output_error() {
             stderr,
         } = if cfg!(target_os = "windows") {
             Command::new("cmd")
-                .args(&["/C", "mkdir ."])
+                .args(["/C", "mkdir ."])
                 .output()
                 .await
                 .unwrap()
@@ -228,7 +228,7 @@ fn test_process_output_error() {
 fn test_finish_once() {
     future::block_on(async {
         let mut prog = if cfg!(target_os = "windows") {
-            Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
+            Command::new("cmd").args(["/C", "exit 1"]).spawn().unwrap()
         } else {
             Command::new("false").spawn().unwrap()
         };
@@ -240,7 +240,7 @@ fn test_finish_once() {
 fn test_finish_twice() {
     future::block_on(async {
         let mut prog = if cfg!(target_os = "windows") {
-            Command::new("cmd").args(&["/C", "exit 1"]).spawn().unwrap()
+            Command::new("cmd").args(["/C", "exit 1"]).spawn().unwrap()
         } else {
             Command::new("false").spawn().unwrap()
         };
@@ -254,7 +254,7 @@ fn test_wait_with_output_once() {
     future::block_on(async {
         let prog = if cfg!(target_os = "windows") {
             Command::new("cmd")
-                .args(&["/C", "echo hello"])
+                .args(["/C", "echo hello"])
                 .stdout(Stdio::piped())
                 .spawn()
                 .unwrap()