doc: Update README.md

Author: jaywcjlove

README.md

@@ -40,14 +40,14 @@ npm install @uiw/react-codemirror --save
 ```jsx mdx:preview
 import React from 'react';
 import CodeMirror from '@uiw/react-codemirror';
-import * as lang from '@codemirror/lang-javascript';
+import { javascript } from '@codemirror/lang-javascript';
 
 function App() {
   return (
     <CodeMirror
       value="console.log('hello world!');"
       height="200px"
-      // extensions={[lang.javascript({ jsx: true })]}
+      extensions={[lang.javascript({ jsx: true })]}
       onChange={(value, viewUpdate) => {
         console.log('value:', value);
       }}