Use matrix strategy with various Node versions in CI

[nkuba]

Currently, we run test job with Node 14 only. It would be nice to run it with multiple Node versions using a matrix strategy.

Consider using cache action,

@nkuba Caching is not added ( Could be added later ) since I am not a fan of catching node_modules directory, but I have added support for various Node versions ( LTS versions only ) for CI on #16