docs: correct typo in installation.mdx (#11258)

Update installation.mdx

Author: RushilJalal

docs/pages/getting-started/installation.mdx

@@ -77,7 +77,7 @@ export const { handlers, signIn, signOut, auth } = NextAuth({
 })
 ```
 
-2. Add an Route Handler under `/app/api/auth/[...nextauth]/route.ts`.
+2. Add a Route Handler under `/app/api/auth/[...nextauth]/route.ts`.
 
 <Callout>
   This file must be an App Router Route Handler, however, the rest of your app