Laravel5.4 消息通知 Notification自定义频道出现这样的问题：
FatalThrowableError in SendcloudChannel.php line 13:
Type error: Argument 2 passed to App\Channels\SendcloudChannel::send() must be an instance of Illuminate\Support\Facades\Notification, instance of App\Notifications\NewUserFollowNotification given, called in /home/vagrant/Code/zhihu-app/vendor/laravel/framework/src/Illuminate/Notifications/NotificationSender.php on line 113
参考文章：
Stackoverflow：How to subscribe user with laravel notification channel for OneSignal
