Return a deferred.

def update_dispute(self, idempotency_key=None, **params):
        """Return a deferred."""
        url = self.instance_url() + '/dispute'
        headers = populate_headers(idempotency_key)
        d = self.request('post', url, params, headers)
        d.addCallback(lambda response: self.refresh_from(
            {'dispute': response}, api_key, True))
        return d.addCallback(lambda _: self.dispute)