🚨 Fix a rust-clippy warning

* https://rust-lang.github.io/rust-clippy/master/#redundant_pattern_matching

examples/02_04_executor/src/lib.rs

@@ -97,7 +97,7 @@ impl Executor {
                 // `Pin<Box<dyn Future<Output = T> + Send + 'static>>`.
                 // We can get a `Pin<&mut dyn Future + Send + 'static>`
                 // from it by calling the `Pin::as_mut` method.
-                if let Poll::Pending = future.as_mut().poll(context) {
+                if future.as_mut().poll(context).is_pending() {
                     // We're not done processing the future, so put it
                     // back in its task to be run again in the future.
                     *future_slot = Some(future);