[docs] Update authentication docs to fix iron-session link. (vercel#3…

…3483)

Co-authored-by: Vincent Voyer <vincent@codeagain.com>
Co-authored-by: Lee Robinson <me@leerob.io>

docs/authentication.md

@@ -62,7 +62,7 @@ export async function getServerSideProps(context) {
 }
 ```
 
-Let's transform the profile example to use [server-side rendering](/docs/basic-features/pages#server-side-rendering). If there's a session, return `user` as a prop to the `Profile` component in the page. Notice there is not a loading skeleton in [this example](https://next-with-iron-session.vercel.app/).
+Let's transform the profile example to use [server-side rendering](/docs/basic-features/pages#server-side-rendering). If there's a session, return `user` as a prop to the `Profile` component in the page. Notice there is not a loading skeleton in [this example](https://iron-session-example.vercel.app/).
 
 ```jsx
 // pages/profile.js