fix sockjs-http-integration

Currently it's not possible to attach a sockJS server instance to an HTTP server instance.

There are two problems this patch is addressing:

1. There is a typo(?) where `vertx.http.HttpServer._to_java_server` won't be defined but instead there is an anonymous function labeled `_to_java_server`.

2. The `httpServer` argument passed to `vertx.sockJS.createSockJSServer` needs to be passed to the `SockJSServer`-constructor.