File to import not found or unreadable: twitter/bootstrap.

[tomoyuki28jp]

https://github.com/tomoyuki28jp/anjlab_bootstrap_rails_test
When I run bundle exec guard command in the project above, I get the following error.

  1) Posts GET /posts works! (now write some real specs)
     Failure/Error: get posts_path
     ActionView::Template::Error:
       File to import not found or unreadable: twitter/bootstrap.
       Load path: /Users/tomo/src/rails/anjlab_bootstrap_rails_test
         (in /Users/tomo/src/rails/anjlab_bootstrap_rails_test/app/assets/stylesheets/application.css)
     # (sass):16
     # ./app/views/layouts/application.html.erb:5:in `_app_views_layouts_application_html_erb___3551402936194681084_70331257069740'
     # ./spec/requests/posts_spec.rb:7:in `block (3 levels) in <top (required)>'