Fix: using path.join instead of concatenate path strings directly.

[PMExtra]

Although Windows API support both forward slash and backslash. But in common sense, Windows should use forward slash as path separator, especially cmd and other command shells usually doesn't support backslash. So the most robust solution is follow the os specified path separator, we can use path.join to implement it.

The most important is that, Lepton has shown the config path in UI (About dialog). For now, it shown mixed path separators in one path, it makes user confused. So I fixed it.

Expected (after this fix):

Actual (before this fix):

[hackjutsu]

That's pretty cool. Thanks for making the change!

[hackjutsu]

@all-contributors please add @PMExtra for code

[allcontributors]

@hackjutsu

I've put up a pull request to add @PMExtra! 🎉