Update .travis.yml to use updated build environments

[liamnichols]

Related: https://docs.travis-ci.com/user/reference/osx/

I came looking for an updated version of PathKit that worked with Xcode 12.5 (1.0.0 is limited because of kylef/Spectre#46) but noticed that it had already been patched in #74. I was going to raise an issue asking for a 1.0.1 release, but I also spotted that .travis.yml could do with a little refresh so here we are 🙂

After considering this change, it would be great if you could do a release so that I have a tag to point to 🙏

Thanks for the hard work!

[liamnichols]

Oooh... TIL builds on travis-ci.org have stopped so maybe there is more to this 😅 I'm not sure what is involved in switching to travis-ci.com though 😄 I could also submit a GitHub Action's workflow?

[kylef]

Apologies for not getting to this sooner.

I could also submit a GitHub Action's workflow?

If you want to peruse this then that sounds great to me. At this point it seems its going to be something that can be relied upon for a long time.

That would also open up being able to test PathKit on Windows. We've had some success testing Commander on Windows in https://github.com/kylef/Commander/blob/master/.github/workflows/windows.yml

[kylef]

I've popped in 2fcd461 which includes a start, but does not test on many platforms or versions. We don't necessarily need to solve everything in one go and can incrementally add additional platforms and versions.