message: Navigated back by popping
  Used currentCrumb to match the android NavigationMotion implementation
diff: @@ -28,6 +28,12 @@ RCT_EXPORT_METHOD(render:(NSInteger)crumb appKey:(NSString *)appKey)
  AppDelegate *delegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
  UINavigationController *navigationController = (UINavigationController *)[UIApplication sharedApplication].keyWindow.rootViewController;
  + NSInteger currentCrumb = [navigationController.viewControllers count] - 1;
  + if (crumb < currentCrumb) {
  + [navigationController popToViewController:navigationController.viewControllers[crumb] animated:true];
  + }
  +
  + if (crumb > currentCrumb) {
  RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:delegate.bridge moduleName:@"ios" initialProperties:@{ @"crumb": [NSNumber numberWithInteger:crumb] }];
  rootView.backgroundColor = [[UIColor alloc] initWithRed:1.0f green:1.0f blue:1.0f alpha:1];
  @@ -35,7 +41,7 @@ RCT_EXPORT_METHOD(render:(NSInteger)crumb appKey:(NSString *)appKey)
  rootViewController.view = rootView;
  rootViewController.title = @"Scene Two";
  [navigationController pushViewController:rootViewController animated:true];
  -
  + }
  }
  @end
  