Used to get a schema from Sovrin
        :param nym: nym that schema is attached to
        :param name: name of schema
        :param version: version of schema
        :return: req object

def requestSchema(self, nym, name, version, sender):
        """
        Used to get a schema from Sovrin
        :param nym: nym that schema is attached to
        :param name: name of schema
        :param version: version of schema
        :return: req object
        """
        operation = { TARGET_NYM: nym,
                      TXN_TYPE: GET_SCHEMA,
                      DATA: {NAME : name,
                             VERSION: version}
        }

        req = Request(sender, operation=operation)
        return self.prepReq(req)