Fix typo in Migration to ActiveStorage

MIGRATING.md

@@ -406,7 +406,7 @@ Then you'll end up with an n+1 as you load each attachment in the loop.
 So while the controller and model will work without change, you will want to
 So while the controller and model will work without change, you will want to
 double-check your loops and add `includes` as needed.
 double-check your loops and add `includes` as needed.
 
 
-ActiveStorage automatically declares `ActiveStorage::Attachement` and
+ActiveStorage automatically declares `ActiveStorage::Attachment` and
 `ActiveStorage::Blob` relationships to your models, along with eager-loading
 `ActiveStorage::Blob` relationships to your models, along with eager-loading
 scopes.
 scopes.