g10k: g10k cache sometimes gets corrupted

From time to time I find that the g10k cache becomes corrupted and I am forced to delete it. This is a big problem in production and ultimately may mean I can’t use g10k in production. A recent example was a failure like this:

executeCommand(): git command failed: git --git-dir /tmp/g10k/git@git.example.com-PUP_puppet-fstab.git remote update --prune exit status 128
Output: fatal: Not a git repository: '/tmp/g10k/git@git.example.com-PUP_puppet-fstab.git'