deleteIssueComment(id, cb) {
      return this._request('DELETE', `/repos/${this.__repository}/issues/comments/${id}`, null, cb);
   }
Delete a comment on an issue
@see https://developer.github.com/v3/issues/comments/#delete-a-comment
@param {number} id - the comment id to delete
@param {Requestable.callback} [cb] - will receive true if the request is successful
@return {Promise} - the promise for the http request