Improve linting compatibility with older git versions
Make linting compatible with Git < v2.22.0 (#26) Some of our CI nodes are still using Ubuntu 18 where Git is old enough to not support `git branch --show-current`.
Make linting compatible with Git < v2.22.0 (#26) Some of our CI nodes are still using Ubuntu 18 where Git is old enough to not support `git branch --show-current`.