Yamllint tests fail if yamllint isn't installed

    Failure/Error: _out, err, _ps = Open3.capture3("yamllint -v")
     
     Errno::ENOENT:
       No such file or directory - yamllint
     # ./app/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder.rb:129:in `yamllint_version'
     # ./app/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder.rb:45:in `header'
     # ./app/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder.rb:59:in `build_comments'
     # ./app/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder.rb:13:in `comments'
     # ./spec/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder_spec.rb:15:in `block (3 levels) in <top (required)>'
     # ./spec/workers/commit_monitor_handlers/commit_range/rubocop_checker/message_builder_spec.rb:21:in `block (3 levels) in <top (required)>'

• We probably shouldn't be shelling out to yamllint during tests
• We should probably handle missing linters better (don't blow up, maybe just skip the linting)