Fix: git.relativize to working repository

The problem I fixed inside git.relativize occurs when user opens a
project folder, which is not directly a root folder, but rather a
subfolder inside repository.
I have left atom.project.relativize there, might be redundant because
the user will always have a repository if they wish to use git.
Merge pull request #86 from markogresak/master

Fix: git.relativize to working repository