use modern nodejs versions

[Meir017]

for reference - https://nodejs.org/en/about/releases/

[ariya]

I definitely agree with the addition of v16, but was there a specific reason to drop v8 and v6 checks?
As long as it doesn't cause a hardship on our part, I don't think we should actively exclude testing those versions.

[Meir017]

@ariya done