Add channel name to NotificationFailed event

Had to look up the source of NotificationFailed and saw that the third parameter should be the name of the channel (https://github.com/laravel/framework/blob/master/src/Illuminate/Notifications/Events/NotificationFailed.php#L40).

Author: casperboone

src/PusherChannel.php

@@ -49,7 +49,7 @@ public function send($notifiable, Notification $notification)
 
         if (! in_array($response['status'], [200, 202])) {
             $this->events->fire(
-                new NotificationFailed($notifiable, $notification, $response)
+                new NotificationFailed($notifiable, $notification, 'pusher-push-notifications', $response)
             );
         }
     }