use QueryStringBuilder for POST requests

Author: fbourigault

lib/Gitlab/Api/AbstractApi.php

@@ -89,7 +89,7 @@ protected function post($path, array $parameters = array(), $requestHeaders = ar
 
         $body = null;
         if (empty($files) && !empty($parameters)) {
-            $body = $this->streamFactory->createStream(http_build_query($parameters));
+            $body = $this->streamFactory->createStream(QueryStringBuilder::build($parameters));
             $requestHeaders['Content-Type'] = 'application/x-www-form-urlencoded';
         } elseif (!empty($files)) {
             $builder = new MultipartStreamBuilder($this->streamFactory);