Use GitRepository::relativize to test if root path
Use GitRepository::relativize to test if root path

GitRepository::relativize handles symlinks and path separator differences
so it is better to use when checking if a path is the working directory

Closes #89

segiddins/fuzzy-finder,atom/fuzzy-finder,Kerruba/fuzzy-finder,nielsAD/fuzzy-finder,pombredanne/fuzzy-finder,gvanderest/fuzzy-finder,nielsAD/fuzzy-finder,viddo/fuzzy-finder,viddo/fuzzy-finder,segiddins/fuzzy-finder,pombredanne/fuzzy-finder,Spy-Seth/fuzzy-finder,Kerruba/fuzzy-finder,Spy-Seth/fuzzy-finder,gvanderest/fuzzy-finder