Oops, update outfit's updated_at when adding/removing items

This bug caused outfit thumbnails to get out of date, because the
outfit's `updated_at` field is used as a cache-busting part of the URL.

app/models/item_outfit_relationship.rb

@@ -1,6 +1,6 @@
 class ItemOutfitRelationship < ApplicationRecord
   belongs_to :item
-  belongs_to :outfit
+  belongs_to :outfit, touch: true
   
   validates_presence_of :item
 end