For people who are still interested in a more streamlined CI/CD experience, the new GitHub actions may be interesting.
It's all build on docker containers, and as such allows you develop in the same container that you're also using for CI/CD.
(I guess this was technically possible with Travis as well, though not as flexible).
In my experience, this has simplified my CI/CD workflow greatly.
I've developed some custom R actions for GitHub actions, and an accompanying ghactions package: