Move to GH Actions

[Nowosad]

I added GitHub Actions to our book. The code was based on our travis file, GitHub Actions of sf, and the ropensci-org/blog-guidance repo. You can learn more about it in the 5. How to deploy a preview of the book for pull requests part of https://ropensci.org/blog/2020/04/07/bookdown-learnings/.

• Ghactions #491

This could be our first step for #476. I think the installation part works already - maybe we now need to update some settings related to Netlify, but I am not sure...

[Nowosad]

https://github.com/Robinlovelace/geocompr/runs/578699757?check_suite_focus=true Awesome!

[Robinlovelace]

The question now: what to do with Travis? I suggest we stop building on Travis and purge the travis set-up stuff. There may be benefits of keeping it but I guess the -s of maintenance time will outweigh the +s of having a backup CI system, GH Actions seems a solid foundation for #476 .

[Nowosad]

Completely agree.