Allow parameters inside of a task to be optional.

I can imagine a few cases where there wouldn't be any parameters needed

parser/src/lib.rs

@@ -26,8 +26,18 @@ mod tests {
                 script {
                     inline = "zypper in -y ${ZAP_PACKAGE}"
                 }
-            }
-        "#;
+            }"#;
+        let _task = TaskParser::parse(Rule::task, buf)
+            .unwrap().next().unwrap();
+    }
+
+    #[test]
+    fn parse_no_parameters() {
+        let buf = r#"task PrintEnv {
+                script {
+                    inline = "env"
+                }
+            }"#;
         let _task = TaskParser::parse(Rule::task, buf)
             .unwrap().next().unwrap();
     }

parser/src/task.pest

@@ -7,7 +7,7 @@ taskfile = _{ SOI
 task = { "task"
         ~ identifier
         ~ opening_brace
-        ~ parameters
+        ~ parameters?
         ~ script
         ~ closing_brace
         }