Today we have many contributions to contrib/offline/ and some PRs
contained invalid coding style for those scripts.
This enables shellcheck to make such invalid coding style easily.
If a branch name contains '.sh', current shellcheck checks the branch
file under .git/ and outputs error because the format is not shell
script one.
This makes shellcheck exclude files under .git/ to avoid this issue.
Kenichi Omichi
Florian Ruynat
Lovro Seder
Maxime Guyot