Tag Wrangling: 500 Error when adding a metatag to a tag that has two levels of subtags

1. Log in as a wrangler

2. Browse > Tags > New Tag

3. Use this form to create four tags, each one a canonical freeform:

   1. Test Tag

   2. Test Tag's Subtag

   3. Test Tag's Metatag

   4. Test Tag's Metatag's Metatag

4. Go to the Edit page for Test Tag's Subtag, fill in Fandoms with "No Fandom" and MetaTags with "Test Tag", and save

5. Go to the Edit page for Test Tag, fill in Fandoms with "No Fandom" and MetaTags with "Test Tag's Metatag", and save

6. Go to the Edit page for Test Tag's Metatag, fill in Fandoms with "No Fandom" and MetaTags with "Test Tag's Metatag's Metatag", and save

What happens
I get a 500 error. If I go back to the edit page, the Fandom has saved, but not the MetaTag.

What should happen
The MetaTag should save correctly, too, and I should end up with a tree like

• Test Tag's Metatag's Metatag

  • Test Tag's Metatag

    • Test Tag

      • Test Tag's Subtag

Notes
The error happens on line 56 of the meta_tagging model: a no method error for update_attribute! because this method does not exist in Rails – only update_attributes, update_attributes!, and update_attribute do.