deleteRelease(id, cb) {
      return this._request('DELETE', `/repos/${this.__fullname}/releases/${id}`, null, cb);
   }
Delete a release
@see https://developer.github.com/v3/repos/releases/#delete-a-release
@param {string} id - the release to be deleted
@param {Requestable.callback} cb - will receive true if the operation is successful
@return {Promise} - the promise for the http request