function dateFormatRSS(dt) {
  return dt.format('DD MMM YYYY HH:mm:ss [GMT]');
}
Formats a moment() object to: DD MMM YYYY HH:mm:ss GMT
Example: 13 Jul 2017 13:31:13 GMT

@param {Object} dt The moment object to export.
@return {string} DD MMM YYYY HH:mm:ss GMT.