fix completion handler constants (#172)

README.md

@@ -142,7 +142,7 @@ And then in your AppDelegate implementation, add the following:
 //Called when a notification is delivered to a foreground app.
 -(void)userNotificationCenter:(UNUserNotificationCenter *)center willPresentNotification:(UNNotification *)notification withCompletionHandler:(void (^)(UNNotificationPresentationOptions options))completionHandler
 {
-  completionHandler(UNAuthorizationOptionSound | UNAuthorizationOptionAlert | UNAuthorizationOptionBadge);
+  completionHandler(UNNotificationPresentationOptionSound | UNNotificationPresentationOptionAlert | UNNotificationPresentationOptionBadge);
 }
 ```