Consider moving from Travis-CI to another CI provider

[jeffaco]

Travis-CI is slowly dying. After the Travis acquisition followed by the significant layoffs, it's prudent to consider a different CI provider.

Two choices are either GitLab CI or CircleCI:

GitLab CI

GitLab CI: GitLab CI provides 50k build minutes/month (Note that the page says that the GitHub integration will be moved from the GitLab.com Free plan to the Silver (paid) plan, but I think that open source projects have all Gold features available to them by default; get clarification GitLib CI is a serious contender).

• GitLab CI Documentation
• The .gitlab-ci.yml config file documentation

CircleCI

CircleCI: CircleCI offers 4 Linux containers with no build limits for open source projects. I've used CircleCI and it was fine, though that was a few years ago.

• CircleCI Documentation

Given that I have prior experience with CircleCI, this is a strong contender unless someone else wants to do the work and has a stronger preference.