BREAKING CHANGE(git): default to `HEAD` git ref instead of`master`

[darcyclarke]

Summary

As more & more organizations adopt new defaults for the default git branch name, we should update hosted-git-info to follow suit.

Exit Criteria

• HEAD is used as the default git ref
• tests are updated to reflect the change
• documentation is updated to reflect the change

Links & References

• Issue: [BUG] npm repo <pkg> assumes a master branch cli#4867
• PR: BREAKING CHANGE: set default git ref to HEAD hosted-git-info#142