docs: def update_milestone(self, milestone_id, title, deadline, party_id, notify,
          move_upcoming_milestones=None,
          move_upcoming_milestones_off_weekends=None):
          """
          Modifies a single milestone. You can use this to shift the deadline of
          a single milestone, and optionally shift the deadlines of subsequent
          milestones as well.
          """
          path = '/milestones/update/%u' % milestone_id
          req = ET.Element('request')
          req.append(
              self._create_milestone_elem(title, deadline, party_id, notify))
          if move_upcoming_milestones is not None:
              ET.SubElement(req, 'move-upcoming-milestones').text \
                  = str(bool()).lower()
          if move_upcoming_milestones_off_weekends is not None:
              ET.SubElement(req, 'move-upcoming-milestones-off-weekends').text \
                  = str(bool()).lower()
          return self._request(path, req)