Update live-code.mdx (#1523)

This costed me a few hours of debugging :)

Author: adrfoong

docs/guides/live-code.mdx

@@ -71,7 +71,7 @@ MDXProvider in the components object so that it is rendered.
 ```js
 // src/App.js
 import React from 'react'
-import {MDXProvider} from '@mdx-js/tag'
+import {MDXProvider} from '@mdx-js/react'
 
 import CodeBlock from './components/CodeBlock'