Как установить гем d3-rails?

Я пытаюсь использовать гем d3.js (https://github.com/iblue/d3-rails), но у меня такая ошибка рельсов (рельсы 5.1.6):

couldn't find file 'd3' with type 'application/javascript'
Checked in these paths: 
  /Users/.../app/assets/config
  /Users/.../app/assets/images
  /Users/.../app/assets/javascripts
  /Users/.../app/assets/stylesheets
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/actioncable-5.1.6/lib/assets/compiled
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/actionview-5.1.6/lib/assets/compiled
  /Users/.../code/agiret/project/caloo/node_modules
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/bootstrap-sass-3.3.7/assets/stylesheets
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/bootstrap-sass-3.3.7/assets/javascripts
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/bootstrap-sass-3.3.7/assets/fonts
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/bootstrap-sass-3.3.7/assets/images
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/font-awesome-sass-4.7.0/assets/stylesheets
  /Users/.../.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/font-awesome-sass-4.7.0/assets/fonts

Кто-нибудь может мне помочь?

Вот мой /app/assets/javascripts/application.js:

//= require jquery
//= require rails-ujs
//= require d3
//= require_tree .

Спасибо.