Retrieves the schema with the given schema_id from the registry
        and returns it as a `dict`.

def get_schema(self, schema_id):
        """
        Retrieves the schema with the given schema_id from the registry
        and returns it as a `dict`.
        """
        res = requests.get(self._url('/schemas/ids/{}', schema_id))
        raise_if_failed(res)
        return json.loads(res.json()['schema'])