---
language: ruby
rvm:
  - 2.2.9
  - 2.3.6
  - 2.4.3
  - 2.5.0
  - ruby-head
  - jruby-9.1.15.0
script: bundle exec rake test

---
language: ruby
rvm:
  - 2.2.9
  - 2.3.6
  - 2.4.3
  - 2.5.0
  - ruby-head
  - jruby-9.1.15.0
before_install:
  - gem update --system
  - gem update bundler
script: bundle exec rake test

Add "gem update --system" before install
Add "gem update --system" before install

ref.
https://github.com/travis-ci/travis-ci/issues/8978#issuecomment-354036443
