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[wai-doi]

Ruby 2.1 or less matrix is not available using a ruby/setup-ruby action.

Run ruby/setup-ruby@v1
  with:
    ruby-version: 2.1
    bundler: default
    working-directory: .
##[error]Unknown version 2.1 for ruby on ubuntu-18.04
        available versions for ruby on ubuntu-18.04: 2.2.10, 2.3.0, 2.3.1, 2.3.2, 2.3.3, 2.3.4, 2.3.5, 2.3.6, 2.3.7, 2.3.8, 2.4.0, 2.4.1, 2.4.2, 2.4.3, 2.4.4, 2.4.5, 2.4.6, 2.4.7, 2.4.9, 2.4.10, 2.5.0, 2.5.1, 2.5.2, 2.5.3, 2.5.4, 2.5.5, 2.5.6, 2.5.7, 2.5.8, 2.6.0, 2.6.1, 2.6.2, 2.6.3, 2.6.4, 2.6.5, 2.6.6, 2.7.0, 2.7.1, head
        File an issue at https://github.com/ruby/setup-ruby/issues if would like support for a new version