fix SimpMessagingTemplate injection in ZuulWebSocketConfiguration.java

[f0rb]

ZuulWebSocketConfiguration needs messagingTemplate to be injected
@Autowired SimpMessagingTemplate messagingTemplate;
which will trigger the invokation of org.springframework.messaging.simp.config.AbstractMessageBrokerConfiguration#brokerMessagingTemplate() and then brokerChannel() and then getBrokerRegistry() and then org.springframework.web.socket.config.annotation.DelegatingWebSocketMessageBrokerConfiguration#configureMessageBroker(MessageBrokerRegistry) and ZuulWebSocketConfiguration has not been initialized yet at that time and the configurers variable has not been injected, and this results ZuulWebSocketConfiguration#configureMessageBroker(MessageBrokerRegistry) never been called.