getElementText(xml, tag) {
    var found = xml.getElementsByTagNameNS("http://purl.org/dc/elements/1.1/", tag);
    var el;
    if (!found || found.length === 0) return "";
    el = found[0];

    if (el.childNodes.length) {
      return el.childNodes[0].nodeValue;
    }

    return "";
  }
Get text of a namespaced element
@private
@param  {node} xml
@param  {string} tag
@return {string} text