Fancy New Dokku Droplet Choking on MySQL (MariaDB)

I followed the instructions of this tutorial: https://www.digitalocean.com/community/articles/how-to-use-the-dokku-one-click-digitalocean-image-to-run-a-ruby-on-rails-app

I installed the MariaDB plugin for Dokku since I’m using MySQL with my app (mostly because I love Sequel Pro). When I get near the end of that tutorial, and I do:

dokku run app rake db:migrate

I get this error:

rake aborted! Specified ‘mysql’ for database adapter, but the gem is not loaded. Add gem 'mysql' to your Gemfile.

(Full error message here: http://d.pr/n/Z5Iy)

As I understand it, Dokku takes care of the database behind the scenes, and there’s no actual Gemfile to edit on the server. My local Rails environment is using ‘mysql2’ in my Gemfile, so it seems there’s some kind of conflict.

Has anyone been able to get MariaDB running on your Dokku droplet? Any idea how I can fix this error? I’ve tried ‘gem install mysql’ to no avail.

Thanks!