code: function setDate(momentInstance, year, month, day) {
      var d = momentInstance._d;
      if (momentInstance._isUTC) {
          /*eslint-disable new-cap*/
          momentInstance._d = new Date(Date.UTC(year, month, day,
              d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds()));
          /*eslint-enable new-cap*/
      } else {
          momentInstance._d = new Date(year, month, day,
              d.getHours(), d.getMinutes(), d.getSeconds(), d.getMilliseconds());
      }
  }
docs: set a gregorian date to moment object
  @param {string} momentInstance
  @param {string} year in gregorian system
  @param {string} month in gregorian system
  @param {string} day in gregorian system