Add deploy keys to projects api (GitLabPHP#157)

* Add deploy keys to projects api

* Coding Style fix

Author: jk

lib/Gitlab/Api/Projects.php

@@ -234,6 +234,15 @@ public function removeMember($project_id, $user_id)
         return $this->delete($this->getProjectPath($project_id, 'members/'.urldecode($user_id)));
     }
 
+    /**
+     * @param int $project_id
+     * @return mixed
+     */
+    public function deployKeys($project_id)
+    {
+        return $this->get($this->getProjectPath($project_id, 'deploy_keys'));
+    }
+
     /**
      * @param int $project_id
      * @param int $page