gio-echo: explicitly close the stream

Not doing so means we rudely disconnect from the socket without clong out our
websocket stream

examples/gio-echo.rs

@@ -15,6 +15,8 @@ async fn run() -> Result<(), Box<dyn std::error::Error>> {
 
     println!("Received: {:?}", msg);
 
+    ws_stream.close(None).await.expect("error sending close");
+
     Ok(())
 }