Fix typo / missing quote in routing guide [ci skip]

Author: carlosantoniodasilva

guides/source/routing.md

@@ -1147,7 +1147,7 @@ resources :photos
 
 This changes the route helpers for `/admin/photos` from `photos_path`,
 `new_photos_path`, etc. to `admin_photos_path`, `new_admin_photo_path`,
-etc. Without the addition of `as: 'admin_photos` on the scoped `resources
+etc. Without the addition of `as: 'admin_photos'` on the scoped `resources
 :photos`, the non-scoped `resources :photos` will not have any route helpers.
 
 To prefix a group of route helpers, use `:as` with `scope`: