fix(git-add): prevent git-add from failing due to open lockfile

With the release of TWBS v3.0.3 the other day, I found out that there are some issues with the git-add strategy in this code... It would benefit from a bit of extra safety...

I still don't want to join too many files into the same git command, so that windows doesn't have any trouble running the script...

The best I can figure is a $timeout, at least without watching the filesystem for a lockfile (which may not be present depending on git version).

This is kind of silly, and there's probably a better way around it, but a timeout it shall be.