language: ruby
rvm:
  - 2.3.0
  - 2.3.1
  - 2.3.2
  - 2.3.3
  - 2.4.0
before_install: gem install bundler -v 1.13.7

language: ruby
rvm:
  - 2.3.3
  - 2.4.0
before_install: gem install bundler -v 1.13.7

Remove Ruby versions lower than 2.3.3 on TravisCI
Remove Ruby versions lower than 2.3.3 on TravisCI

ref. https://www.ruby-lang.org/ja/news/2016/11/21/ruby-2-3-3-released/
