Switch to os.homedir() when we move to v4+

[nfischer]

NodeJS added support for os.homedir() to get the user's home directory in a reliable way. When we drop support for v4, let's switch to that to reduce the amount of code we need to maintain.

[freitagbr]

If os.homedir is not reliant on native code, maybe we could polyfill it?

[nfischer]

We already have our own implementation. I was suggesting we remove that implementation once we switch to v4+.

[nfischer]

Already fixed in #725