fix for reading config for branches with dot in name

When using "git-tfs labels" I got some errors due to the naming of my branches.
I had a branch named after a maintenance version ("maint-1.0.0.0") and since when reading the config a split is done on dot.
I did a quickfix of it. The best options would to not split on dot but that was more work and seemed to require work in libgit2sharp as well. 

git-tfs is a great tool by the way :+1: !