message: fixed backend on_change
diff: @@ -43,9 +43,12 @@ async fn on_change(mut receiver: UnboundedReceiver<()>, release: bool, https: bo
  if let Some(build_task) = build_task.take() {
  build_task.abort();
  }
  - if let Some(mut server) = server.lock().take() {
  - let _ = server.kill();
  +
  + let server_process = { server.lock().take() };
  + if let Some(mut server) = server_process {
  + let _ = server.kill().await;
  }
  +
  build_task = Some(spawn(build_and_run(Arc::clone(&server), release, https)));
  }
  