docs(GA demo): use google analytics 4

demo/index.html

@@ -62,7 +62,7 @@
       m.parentNode.insertBefore(a, m)
     })(window, document, 'script', 'https://www.google-analytics.com/analytics.js', 'ga');
 
-    ga('create', 'UA-99119327-1', 'auto');
+    ga('create', 'G-T158HYBVZ2', 'auto');
     ga('send', 'pageview');
   </script>
 </body>