Use just `process.env.USERPROFILE` for user's home folder on Windows

Removed reference to `%HOMEPATH%`, because it doesn't contain a drive
spec. (e.g., it contains only `\Users\Jdoe` rather than `C:\Users\Jdoe`),
whereas `%USERPROFILE%` _does_ include the drive spec., which makes it the
better choice - and the only variable required to support all flavors of Windows.