ci: setup GitHub Actions

[nogic1008]

Note: To take advantage of this PR, you need to enable GitHub Actions on this repository.
sample jobs

• Setup GitHub Actions workflow
  • Node.js 10, 12, 14
  • Jest 24, 25, 26
• bump @babel/core and @babel/preset-env to 7.9.0 to fix error in Node.js 12 or above

[lmiller1990]

Interesting. Is there an advantage to GH actions over Circle CI for example?

[nogic1008]

@lmiller1990

Advantage:

• Circle CI cannot watch test results without signing up, but GitHub Actions can do.
• Circle CI can also use matrix jobs, but free plan don't run in parallel. It will take more time.
• Testing can be done even in forked repositories. (need to opt in there)
• Lots of reusable actions (like orb in Circle CI) are available in the community.

Disadvantage:

• GitHub Actions cannot rerun job partially. only can "Rerun All".
• It is difficult to access the running job with SSH etc.

[lmiller1990]

Sounds like we should ues GH actions. I will look into this on the weekend. Thanks!

[nogic1008]

@lmiller1990
Thank you for your interest.
This PR conflicts with #284, so I'll rebase it after 284 has been merged.

[nogic1008]

@lmiller1990
Ready to merge. After merged, we can delete /.circleci folder safely.
GitHub Actions result

[lmiller1990]

Forgot this, sorry! I sent you a msg on Twitter regarding this PR, let's chat.

[lmiller1990]

Thanks @nogic1008, feel free to make any other improvements you see, I can review your PRs :)