Update next-js.mdx

Author: tinhochu

docs/docs/getting-started/next-js.mdx

@@ -38,7 +38,7 @@ This is all we need installed to create our first Queue!
 <Tabs>
 <TabItem value="app" label="App Router">
 
-Create a new [Router Handler](https://nextjs.org/docs/app/building-your-application/routing/router-handlers) at `app/api/queues/email.js` and paste the following:
+Create a new [Router Handler](https://nextjs.org/docs/app/building-your-application/routing/router-handlers) at `app/api/queues/email/route.ts` and paste the following:
 
 ```typescript title="app/api/queues/email/route.ts"
 import { Queue } from "quirrel/next-app"