use a hash for yaml stuff

app/models/issue.rb

@@ -392,7 +392,7 @@ class Issue < ActiveRecord::Base
   def attachment_removed(obj)
     init_journal(User.current)
     create_journal
-    last_journal.update_attribute(:changed_data, {"attachments_" + obj.id.to_s => [obj.filename, nil]}.to_yaml)
+    last_journal.update_attribute(:changed_data, {"attachments_" + obj.id.to_s => [obj.filename, nil]})
   end
 
   # Return true if the issue is closed, otherwise false