Method checkFileOrder

/**
 * Method that takes two paths and checks if the files exist with different order
 *
 * @param   string  $first   the path of the minified file
 * @param   string  $second  the path of the non minified file
 *
 * @return  string
 *
 * @since  4.0.0
 */
private static function checkFileOrder($first, $second)
{
    if (is_file($second)) {
        return static::convertToRelativePath($second);
    }
    if (is_file($first)) {
        return static::convertToRelativePath($first);
    }
    return '';
}