public function addMap($iterable, \Closure $step, $name)
 {
     $sitemap = new Sitemap($iterable, $step);
     $sitemap->setHost($this->host);
     if ($this->limit > 0) {
         $url = dirname($this->url . '/' . $name);
         $file = explode(".", basename($name));
         $ext = array_pop($file);
         $url = $url . '/' . implode(".", $file) . '-%d.' . $ext;
         $sitemap->multipleFiles($url, $this->limit);
     }
     $sitemap->generate($this->dir . '/' . $name);
     return $this;
 }