Automatic testing via GitHub Actions

[kokes]

This PR introduces automated testing on each pull request and commit. This is to simplify development flows for people without suitable dev environments.

I have two questions:

1. Tests are triggered using Node 10 and 12 (v14 failed), are there any other versions we want to test against? The README doesn't quite describe what environments are supported.
2. Do we want to test other things? Like a production build?

Thanks!

[captainsafia]

Wow! Thanks so much for contributing this. I've been trying to get around to using GitHub Actions as CI in a few repos and this example is a great one to work off of.

Tests are triggered using Node 10 and 12 (v14 failed), are there any other versions we want to test against? The README doesn't quite describe what environments are supported.

Testing the current LTS versions of Node seems like a sensible plan. Any chance you have the stacktrace for the failure on v14?

Do we want to test other things? Like a production build?

yarn test and yarn build:all are good things to include in the CI steps.

[kokes]

1. Yup, the stacktrace is in my actions.
2. When installing on 10/12, I'm told npm WARN deprecated [email protected]: Chokidar 2 will break on node v14+. Upgrade to chokidar 3 with 15x less dependencies., so that will be an issue as well. I traced this a few days ago through babel/cli and watchpack and I hit a few beta packages, so I'm not sure it's ready to be updated yet.
3. While this issue originally popped on my local machine (macOS, Node v14.2.0), I can't quite replicate it now, it builds, though the stack trace should give us something to follow.
4. I added a build:all to the yaml file and it passed (again, see my actions).
5. Sadly, act (local CI) might be broken due to a parsing issue.

[willingc]

Thanks @kokes 😄 This is good stuff.

@captainsafia I'm going to go ahead and merge. v14 can be iterated on in a future PR.