language: ruby
jobs:
  include:
    - rvm: 1.9.3
    - rvm: 2.0.0
    - rvm: 2.1
    - rvm: 2.2
    - rvm: 2.3
    - rvm: 2.4
      env: RUBYOPT="--enable-frozen-string-literal"
    - rvm: 2.5
      env: RUBYOPT="--enable-frozen-string-literal"
    - rvm: ruby-head
      env: RUBYOPT="--enable-frozen-string-literal"
before_install:
  # 1. The pre-installed Bundler version on Travis is very old; causes 1.9.3 build issues
  # 2. Bundler 2.0 is not supported by the whole matrix
  - gem install bundler -v'< 2'

script:
  -  bundle exec rake