listGists(cb) {
      return this._request('GET', this.__getScopedUrl('gists'), null, cb);
   }
List the user's gists
@see https://developer.github.com/v3/gists/#list-a-users-gists
@param {Requestable.callback} [cb] - will receive the list of gists
@return {Promise} - the promise for the http request