added default channel parameter when constructing own notification (firebase#326)

Author: maxost

messaging/app/src/main/java/com/google/firebase/quickstart/fcm/MyFirebaseMessagingService.java

@@ -114,8 +114,10 @@ private void sendNotification(String messageBody) {
         PendingIntent pendingIntent = PendingIntent.getActivity(this, 0 /* Request code */, intent,
                 PendingIntent.FLAG_ONE_SHOT);
 
+        String channelId = getString(R.string.default_notification_channel_id);
         Uri defaultSoundUri= RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
-        NotificationCompat.Builder notificationBuilder = new NotificationCompat.Builder(this)
+        NotificationCompat.Builder notificationBuilder =
+                new NotificationCompat.Builder(this, channelId)
                 .setSmallIcon(R.drawable.ic_stat_ic_notification)
                 .setContentTitle("FCM Message")
                 .setContentText(messageBody)