Using standardised value for stomp (as WebSocket Protocol)

the v11.stomp value is the one that is registered / IANA:
http://www.iana.org/assignments/websocket/websocket.xml

Also the HornetQ broker uses that:
https://github.com/hornetq/hornetq/blob/master/hornetq-server/src/main/java/org/hornetq/core/protocol/stomp/WebSocketServerHandler.java#L84