Bug(?) Fix : When plugin execute purge_invalid() of PageCache.php

    public function purge_invalid()
    {
        //$files = glob($this->get_key() . ".*");
	    $files = glob($this->cache->get_dir() . "/" . $this->cache->get_url_hash() . ".*");
        foreach ($files as $file) {
            unlink($file);
        }
    }