Fix build error

- was getting `undefined method assets` when trying to build transition in docker
- followed this advice to fix the problem: https://stackoverflow.com/questions/50984265/ruby-on-rails-console-undefined-method-assets

config/application.rb

@@ -13,6 +13,7 @@
 require "action_view/railtie"
 # require "action_cable/engine"
 require "rails/test_unit/railtie"
+require "sprockets/railtie"
 
 # Require the gems listed in Gemfile, including any gems
 # you've limited to :test, :development, or :production.