updated react example to v18

Author: maxschwarzmueller

code/react-vs-vanilla-js-example/react/src/index.js

@@ -1,5 +1,5 @@
 import React from 'react';
-import ReactDOM from 'react-dom';
+import ReactDOM from 'react-dom/client';
 
 import './index.css';
 import App from './App';