editMilestone(milestone, milestoneData, cb) {
      return this._request('PATCH', `/repos/${this.__repository}/milestones/${milestone}`, milestoneData, cb);
   }
Edit a milestone
@see https://developer.github.com/v3/issues/milestones/#update-a-milestone
@param {string} milestone - the id of the milestone to edit
@param {Object} milestoneData - the updates to make to the milestone
@param {Requestable.callback} [cb] - will receive the updated milestone
@return {Promise} - the promise for the http request