Update dependencies to napi versions to support Node 12

[baparham]

I was looking for node 12 support and this seemed to work so I thought I would file a PR to see if you think it should go into the main repo.

[baparham]

Seems like perhaps the CI file should also be updated to test against node 12. I can push another commit that will hopefully address that

[zbynek]

This (+ some unrelated code cleanup) was already proposed in #62

[baparham]

Thanks for engaging @zbynek - I can see that the other requests have been open a while, is it basically just held up with the maintainer(s)?

I also had the thought that perhaps a -napi fork of windows-registry should be published to the registry so that users might choose between the NAPI enabled version and this one depending on their node versions, but it seems like fixing this one and making it backward compatible with currently support node versions seems to make the most sense. Thoughts?

[simonbuchan]

If there's interest, I did end up writing an NAPI package native-reg after opening #62, but be warned it has an incompatible C-style API at the moment, so it's not drop-in. I'm happy to take requests, including API changes though.