Hook brokes merging state

[timocov]

If you run git-pylint-commit-hook when you are in merging (for example when you have conflicts) you will missed merging state.
Possible reason is using stash

[evanunderscore]

I initially added the stash in order to fix #26, but I no longer think this is good default behavior. I haven't looked into this particular problem, but I think it would be a good idea to make the stashing opt-in regardless.

[sebdah]

A fix for this (#56) has been released in version 2.3.0.