[Net] Change server in the websocket demo.

The old server (echo.websocket.org) is no longer active.
The new server (libwebsockets.org) is the demo server of another popular
websocket library (LWS) which we also previously used.

tutorials/networking/websocket.rst

@@ -37,7 +37,7 @@ This example will show you how to create a WebSocket connection to a remote serv
     extends Node
 
     # The URL we will connect to
-    export var websocket_url = "ws://echo.websocket.org"
+    export var websocket_url = "wss://libwebsockets.org"
 
     # Our WebSocketClient instance
     var _client = WebSocketClient.new()
@@ -53,7 +53,7 @@ This example will show you how to create a WebSocket connection to a remote serv
         _client.data_received.connect(_on_data)
 
         # Initiate connection to the given URL.
-        var err = _client.connect_to_url(websocket_url)
+        var err = _client.connect_to_url(websocket_url, ["lws-mirror-protocol"])
         if err != OK:
             print("Unable to connect")
             set_process(false)