fix: Resolve dependency issues on Node.js 20

[jduncanator]

This bumps dependencies to resolve installation issues with Node 20. It also drops the native module and makes use of fs.statfs where available (Node.js >=18).

Ideally we wouldn't require node-gyp, or the native module at all when installing under supported engines, but there doesn't seem to be an elegant way to achieve that, and I don't want to drop support for Node <18 (yet).

This supersedes #61, and should resolve #60 and #59. @francois-spectre and @radjybaba, testing would be appreciated to confirm this fixes your issues!

Resisting the urge to type const, use object destructuring, and lambdas whilst making this change was very hard... it hurts my eyes (and my soul).

[jduncanator]

I've verified these changes work all the way back to Node 4.9.1 (on Linux):

root@c66171b3c386:~/node-diskusage# node
> process.version
'v4.9.1'
> require('.').checkSync('/')
{ available: [...],
  free: [...],
  total: [...] }
>

Node 6.17.1 (on Linux):

root@734831f2b9b3:~/node-diskusage# node
> process.version
'v6.17.1'
> require('.').checkSync('/')
{ available: [...],
  free: [...],
  total: [...] }
>

As well as in Node 20.6.1 (on Windows):

> process.version
'v20.6.1'
> require('.').checkSync('C:')
{ available: [...], free: [...], total: [...] }
>

I'm unable to get Node 0.12 to work, I struggle to even install node-gyp as a dep, not sure if it's always been that way or something I've broken with this change, but I don't mind dropping support for 0.12 😅

[jduncanator]

Turns out the Docker image I was using was broken. Using node:0.12, I'm able to build and verify everything still works all the way back to Node 0.12.18:

root@6aa0edf4a485:~/node-diskusage# node
> process.version
'v0.12.18'
> require('./').checkSync('/')
{ available: [...],
  free: [...],
  total: [...] }

Unless anyone has objections or issues, I'll merge this in the morning (~9 hours from now)!