Ruby 2.0-2.3 fails to install at macOs 10.13

[native-api]

Since the reason is the job running very slowly, I believe this is a case of

Build delays for open source project

As was pointed out in Builds hang in queued state - #6 by Montana linked to earlier in this topic, Travis is moving workers from travis-ci.org to travis-ci.com in preparation to fully close .org (or rather, make it read-only) around the New Year. So you need to migrate to .com to stop experiencing delays. Note the caveats: