Update Server.java

Adjuste rename from websocketHandler to webSocketHandler

eclipse-vertx/vert.x#3235

Author: aaloise

core-examples/src/main/java/io/vertx/example/core/http/websockets/Server.java

@@ -15,7 +15,7 @@ public static void main(String[] args) {
 
   @Override
   public void start() throws Exception {
-    vertx.createHttpServer().websocketHandler(ws -> ws.handler(ws::writeBinaryMessage)).requestHandler(req -> {
+    vertx.createHttpServer().webSocketHandler(ws -> ws.handler(ws::writeBinaryMessage)).requestHandler(req -> {
       if (req.uri().equals("/")) req.response().sendFile("ws.html");
     }).listen(8080);
   }