Change the milestone of an issue.
        :param issue_id: the id of the issue
        :param milestone: the new milestone for the issue
            (set None to remove milestone)
        :return:

def change_issue_milestone(self, issue_id, milestone):
        """
        Change the milestone of an issue.
        :param issue_id: the id of the issue
        :param milestone: the new milestone for the issue
            (set None to remove milestone)
        :return:
        """
        request_url = "{}issue/{}/milestone".format(self.create_basic_url(),
                                                    issue_id)

        payload = {} if milestone is None else {'milestone': milestone}

        return_value = self._call_api(request_url,
                                      method='POST', data=payload)

        LOG.debug(return_value)