Fix typo in API Routes documentation. (#10054)

Co-authored-by: JJ Kasper <jj@jjsweb.site>

docs/api-routes/introduction.md

@@ -25,7 +25,7 @@ For example, the following API route `pages/api/user.js` handles a simple `json`
 export default (req, res) => {
   res.statusCode = 200
   res.setHeader('Content-Type', 'application/json')
-  res.end(JSON.stringify({ name: 'Jhon Doe' }))
+  res.end(JSON.stringify({ name: 'John Doe' }))
 }
 ```