Prevent fatal error in JsonRpc-Client

Zend\Server\Json\Response passes the json_decode()'d server response to its method setOptions(), which is type hinted as array. If the server response is anything but an array, this leads to a fatal error.

Maybe the Response class should be altogether more strict in its parsing of the response, but for now I just throw a RuntimeException, as pretty much anything is preferable to a fatal error.