title: didReceiveRemoteNotification not called when Firebase is used along with Push framework
body: <p>I am using <code>Firebase</code> for analytics and a library for push notifications. When I use either of them, <strong>didReceiveRemoteNotification</strong> get called. But when I use them both together, <strong>didReceiveRemoteNotification</strong> doesn't get called.<br>
  Code :  </p>
  
  <p><strong>didFinishLaunchingWithOptions</strong> :</p>
  
  <pre><code>NSString *google_app_id = @"----";
      NSString *gcm_sender_id = @"----";
      FIROptions *o = [[FIROptions alloc] initWithGoogleAppID:google_app_id GCMSenderID:gcm_sender_id];
      o.APIKey = @"----";
      o.bundleID = @"----";
      o.clientID = @"----";
      [FIRApp configureWithOptions:o];  
  
  // Initilization of push framework 
  </code></pre>
  
  <p><strong>didReceiveRemoteNotification</strong> :  </p>
  
  <pre><code>- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
      // This method is not called when Firebase and push framework are enabled at the same time
      // It works fine when only Firebase or only push framework is enabled
      NSLog(@"Push: %@", userInfo);
  }
  </code></pre>