Update platform-channels.md (#2939)

* Update platform-channels.md

Updated platform-channels.md to reflect changes to the new implementation of binaryMessenger.

* Update AUTHORS

Author: GianlucaCesari

AUTHORS

@@ -8,3 +8,4 @@ Faisal Abid <faisal.abid@gmail.com>
 Iiro Krankka <iiro.krankka@gmail.com>
 Ryuji Iwata <qt.luigi@gmail.com>
 Novoda Ltd. — www.novoda.com (Niamh Power, Sebastiano Poggi)
+Gianluca Cesari <giangi.ces@gmail.com>

src/docs/development/platform-integration/platform-channels.md

@@ -579,9 +579,9 @@ a `FlutterMethodChannel` tied to the channel name
 
     let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
     let batteryChannel = FlutterMethodChannel(name: "samples.flutter.dev/battery",
-                                              binaryMessenger: controller)
+                                              binaryMessenger: controller.bynaryMessenger)
     batteryChannel.setMethodCallHandler({
-      (call: FlutterMethodCall, result: FlutterResult) -> Void in
+      (call: FlutterMethodCall, result: @escaping FlutterResult) -> Void in
       // Note: this method is invoked on the UI thread.
       // Handle battery messages.
     })
@@ -724,4 +724,4 @@ DispatchQueue.main.async {
 
 [block]: https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/WorkingwithBlocks/WorkingwithBlocks.html
 
-[dispatch queue]: https://developer.apple.com/documentation/dispatch/dispatchqueue
+[dispatch queue]: https://developer.apple.com/documentation/dispatch/dispatchqueue