Changed the visibility of the method \LaravelFCM\Sender\FCMSender::po…

…st, from private to protected in order to be able to override it

src/Sender/FCMSender.php

@@ -105,7 +105,7 @@ public function sendToTopic(Topics $topics, Options $options = null, PayloadNoti
      *
      * @return null|\Psr\Http\Message\ResponseInterface
      */
-    private function post($request)
+    protected function post($request)
     {
         try {
             $responseGuzzle = $this->client->request('post', $this->url, $request->build());