private function registerCourier()
    {
        $this->app->bind('CodeZero\Courier\Courier', function($app)
        {
            $curlRequest = $app->make('CodeZero\Curl\Request');
            $responseParser = $app->make('CodeZero\Courier\CurlResponseParser');
            $cache = $app->make('CodeZero\Courier\Cache\Cache');

            return new CurlCourier($curlRequest, $responseParser, $cache);
        });
    }