title: How to fix: "No visible @interface for 'FIRInstanceID' declares the selector 'token'" in iOS build in Flutter
body: <p>The problem occurred when I tried to build the iOS version of my flutter app that uses Firebase Messaging after updating Firebase pod to 6.0.1. I never use Objecrtive C this is why this error is confusing</p>
  
  <p>I can get it to work by just commenting out the line that causes the problem. I'm not sure how important it is to have this piece of code for production.</p>
  
  <pre><code>- (void)application:(UIApplication *)application
  didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken {
  #ifdef DEBUG
  [[FIRMessaging messaging] setAPNSToken:deviceToken    type:FIRMessagingAPNSTokenTypeSandbox];
  #else
  [[FIRMessaging messaging] setAPNSToken:deviceToken  type:FIRMessagingAPNSTokenTypeProd];
  #endif
  //[_channel invokeMethod:@"onLaunch" arguments:_launchNotification];
  [_channel invokeMethod:@"onToken" arguments:[[FIRInstanceID instanceID] token]];
  }
  </code></pre>
  
  <p>Expected result is just building the app but I get the error.</p>