Change screenChange eventName key to id (#804)

ios/RCCViewController.m

             [[[RCCManager sharedInstance] getBridge].eventDispatcher sendAppEventWithName:rootView.appProperties[@"navigatorEventID"] body:@
              {
                  @"type": @"ScreenChangedEvent",
-                 @"method": eventName
+                 @"id": eventName
              }];
         }
     }