Update the group's membership

        :type group_id: int
        :param group_id: Group ID Number

        :type users: list of str
        :param users: List of emails

        :rtype: dict
        :return: dictionary of group information

def update_membership(self, group_id, users=[]):
        """
        Update the group's membership

        :type group_id: int
        :param group_id: Group ID Number

        :type users: list of str
        :param users: List of emails

        :rtype: dict
        :return: dictionary of group information
        """
        data = {
            'groupId': group_id,
            'users': users,
        }
        return _fix_group(self.post('updateMembership', data))