'Update this reference.
:param str sha: (required), sha of the reference
:param bool force: (optional), force the update or not
:returns: bool'

@requires_auth
def update(self, sha, force=False):

    data = {u'sha': sha, u'force': force}
    json = self._json(self._patch(self._api, data=dumps(data)), 200)
    if json:
        self._update_attributes(json)
        return True
    return False
