docs(useWebSocket): update test url (#2209)

Author: liuyib

packages/hooks/src/useWebSocket/demo/demo1.tsx

@@ -12,7 +12,7 @@ export default () => {
   const messageHistory = useRef<any[]>([]);
 
   const { readyState, sendMessage, latestMessage, disconnect, connect } = useWebSocket(
-    'wss://demo.piesocket.com/v3/channel_1?api_key=VCXCEuvhGcBDP7XhiJJUDvR1e1D3eiVjgZ9VRiaV&notify_self',
+    'wss://ws.postman-echo.com/raw',
   );
 
   messageHistory.current = useMemo(