Migrate away from travis-ci.org

[slonopotamus]

travis-ci.org is going to be shut down on December, 31:

https://docs.travis-ci.com/user/migrate/open-source-repository-migration#frequently-asked-questions

Q. When will the migration from travis-ci.org to travis-ci.com be completed?
A. In an effort to ensure that all of our users - whether you build open-source, public or private repositories - receive regular feature updates, security patches and UX/UI enhancements, we are announcing that travis-ci.org will be officially closed down completely no later than December 31st, 2020, allowing us to focus all our efforts on bringing new features and fixes to travis-ci.com and all of our awesome users like yourself on the travis-ci.com domain.

Q. What will happen to travis-ci.org after December 31st, 2020?
A. Travis-ci.org will be switched to a read-only platform, allowing you to see your jobs build history from all repositories previously connected to travis-ci.org.

Also, note that travis-ci.com, while being the most logical place to move to, has build time limits for public repositories:

https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing

For those of you who have been building on public repositories (on travis-ci.com, with no paid subscription), we will upgrade you to our trial (free) plan with a 10K credit allotment (which allows around 1000 minutes in a Linux environment).

[slonopotamus]

Do not forget to update build.gradle.kts:

val gitCommit = System.getenv("TRAVIS_COMMIT") ?: ""