Upgrade acts-as-taggable-on to 4.0.0
This is a blocker for Rails 5, #14286 (moved).
Changelog for 4.0.0: https://github.com/mbleigh/acts-as-taggable-on/blob/master/CHANGELOG.md#400--2016-08-08
After upgrading acts-as-taggable-on to 4.0.0, the post-install message says to run rake acts_as_taggable_on_engine:install:migrations
. Doing so causes two migrations to be created. I'm not sure how we use acts-as-taggable-on or whether we should be using these migrations, so I don't want to do this upgrade for fear of breaking something :)
If someone else could handle this, it'd be appreciated.