Prevenir cache de CSS

url_fresh.php

function url_fresh($url = '', $echo = true){ //http://css-tricks.com/snippets/wordpress/prevent-css-caching/
    if($echo){
        echo get_stylesheet_directory_uri().'/'.$url.'?r='.filemtime( get_stylesheet_directory().'/'.$url);
    }else{
        return get_stylesheet_directory_uri().'/'.$url.'?r='.filemtime( get_stylesheet_directory().'/'.$url);
    }
}

function carrega_scripts() {
    wp_register_script('bootstrap', url_fresh('js/vendor/bootstrap.min.js',false),array('jquery'),false,false);
    wp_enqueue_script('bootstrap');
}
add_action('wp_enqueue_scripts', 'carrega_scripts');