Updated creating an instance of the GrantedController to not force th…

…e client_credentials storage.

src/OAuth2/Server.php

@@ -159,7 +159,7 @@ public function getGrantController()
             if (0 == count($this->grantTypes)) {
                 $this->grantTypes = $this->getDefaultGrantTypes();
             }
-            $this->grantController = new OAuth2_Controller_GrantController($this->storages['client_credentials'], $this->accessTokenResponseType, $this->grantTypes);
+            $this->grantController = new OAuth2_Controller_GrantController(reset($this->storages), $this->accessTokenResponseType, $this->grantTypes);
         }
         return $this->grantController;
     }