The command bin/test stop running single tests once Devise started to
support Rails 5.2. The problem is because we used `rails/test_unit/minitest_plugin`
and this file was moved to another place.
See: https://github.com/rails/rails/pull/29572
I'm not sure if we should require the `minitest-plugin` directly from
Rails like we were doing, I tried it and it didn't work. So I'm
changing this `bin/test` completely based on how Rails does that [here](https://github.com/rails/rails/blob/master/tools/test.rb)