Not scan files on git version < 1.8.5 #220
Description
Git version before 1.8.5 does not support -C <path> option.
When running detect-secrets with pre-1.8.5 git version, _get_git_tracked_files would return None since the exception is silently ignored. This causes non of the tracked files been scanned.
git help on 1.8.3
$ git help
usage: git [--version] [--help] [-c name=value]
[--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
[-p|--paginate|--no-pager] [--no-replace-objects] [--bare]
[--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
<command> [<args>]