private function version4($version = false)
    {
        if (!env('APP_CDN', true)) {
            FrontendAsset::add('vendor/font-awesome/css/font-awesome.min.css');

            return;
        }

        $version = FrontendAsset::version(class_basename(__CLASS__), $version);
        FrontendAsset::add('https://maxcdn.bootstrapcdn.com/font-awesome/'.$version.'/css/font-awesome.min.css');
    }