Fix docs about etag

actionpack/lib/action_controller/metal/conditional_get.rb

@@ -25,7 +25,7 @@ module ActionController
       #     def show
       #       # Etag will differ even for the same invoice when it's viewed by a different current_user
       #       @invoice = Invoice.find(params[:id])
-      #       fresh_when(@invoice)
+      #       fresh_when etag: @invoice
       #     end
       #   end
       def etag(&etagger)