Fix (un)subscribe operation. The http (un)subscription request was ne…

…ver sent to the hub

src/PubSubHubbub/Subscriber.php

@@ -625,7 +625,7 @@ protected function _doRequest($mode)
             }
             $client->setUri($url);
             $client->setRawBody($this->_getRequestParameters($url, $mode));
-            $response = $client->getResponse();
+            $response = $client->send();
             if ($response->getStatusCode() !== 204
                 && $response->getStatusCode() !== 202
             ) {