Add CI to run tests for old Node.js versions

[ai]

We need to support at least the current Node.js versions: 14, 16, 18.

It will be easier to add color.js if we will support Node.js 12 for a some time.

I suggest using Github Action since it is free and has a good integration to Github.

[LeaVerou]

I fully support this.

colorjs is actually hosted on Netlify, which is even more powerful than Github Actions :)

[ai]

Am I right that Netlify is a hosting, not CI? Can we run tasks there and see the tasks status in PR?

[LeaVerou]

Yes, absolutely! That's one of the main things Netlify does!