On Windows, root package is not ignored and gets treated as a dependency

[DanielOaks]

Under Windows, say that I run this on my package github.com/DanielOaks/oragono, vendetta will then try to vendor my package github.com/DanielOaks/oragono under vendor/github.com/DanielOaks/oragono.

Basically, I think it just doesn't recognise that the root package is actually the root package because of Windows slashes and all. I'll do some more testing to see what's up, works great on my OSX system though!