$ bundle install --path=vendor/bundle
:
An error occurred while installing nio4r (2.1.0), and Bundler cannot
continue.
Make sure that `gem install nio4r -v '2.1.0' --source 'https://rubygems.org/'`
succeeds before bundling.
In Gemfile:
rails-settings-cached was resolved to 0.6.6, which depends on
rails was resolved to 5.1.4, which depends on
actioncable was resolved to 5.1.4, which depends on
nio4r
これでもいっしょよねえ