public static function shorten($url)
    {
        $client = new Client();
        $request = $client->get(self::$_BITLY_URL);
        $request->getQuery()->add('access_token', self::$_ACCESS_KEY);
        $request->getQuery()->add('longUrl', $url);
        $resp = $request->send();
        $jsonRep = $resp->json();
        return $jsonRep['data']['url'];
    }