增加objc支持

ios/Classes/CLXListenerScreenPlugin.swift

@@ -2,7 +2,7 @@ import Flutter
 import UIKit
 import Photos
 
-public class CLXListenerScreenPlugin: NSObject, FlutterPlugin {
+@objcMembers public class CLXListenerScreenPlugin: NSObject, FlutterPlugin {
     
     var _eventSink: FlutterEventSink?;