Fix bug in calling pause or resume in web builds.

Author: timbotimbo

example/unity/DemoApp/Assets/FlutterUnityIntegration/Editor/Build.cs

@@ -285,7 +285,7 @@ private static void ModifyWebGLExport()
         });
 
         window.parent.addEventListener('unityFlutterBidingFnCal', function (args) {
-            mainUnityInstance.SendMessage('GameManager', 'HandleWebFnCall', args);
+            mainUnityInstance.SendMessage('GameManager', 'HandleWebFnCall', args.data);
         });
         ");