git -C option is not yet available on git version 1.8.3.1
Unknown option: -C
usage: git [--version] [--help] [-c name=value]
[--exec-path[=
[-p|--paginate|--no-pager] [--no-replace-objects] [--bare]
[--git-dir=
WARN: continuing with clone
s/no more used/not yet available/
As mentioned in a comment on #20, git -C was only introduced in 1.8.5.
I can only find a handful of distros with git < 1.8.5. Of those, only CentOS 7 (which matches the git version you have) appears to not yet have reached EOL, but it will be entering "the Maintenance updates phase, only Security errata and select mission critical bug fixes will be released" by the end of year.
I closed #20 primarily due to lack of response, but (now that I figured by myself out why someone could be [reasonably] stuck on such an old version of git) I'll try to remember to include the fix next time I'm working on this codebase.
With #22, support for git 1.8.3.1 will now also require doing something about --prune-tags, which is a fairly recent addition to git.