🐛 open safariViewController from main thread

implement fix from fullstackreact#150

Author: blakek

ios/OAuthManager/OAuthManager.m

@@ -88,9 +88,11 @@ + (BOOL)setupOAuthHandler:(UIApplication *)application
     [authPlatform setURLOpener: ^void(NSURL *URL, DCTAuthPlatformCompletion completion) {
         // [sharedManager setPendingAuthentication:YES];
         if ([SFSafariViewController class] != nil) {
+          dispatch_async(dispatch_get_main_queue(), ^{
             safariViewController = [[SFSafariViewController alloc] initWithURL:URL];
             UIViewController *viewController = application.keyWindow.rootViewController;
             [viewController presentViewController:safariViewController animated:YES completion: nil];
+          });
         } else {
             [application openURL:URL];
         }