public function updateGroup (Group $group)
    {
        $json = [
            'group' => [
                'id'   => $group->getID(),
                'name' => $group->getName(),
            ],
        ];

        $request = new Request("POST", "https://api.weixin.qq.com/cgi-bin/groups/update", [], json_encode($json));
        $this->client->send($request);
    }