Remove implict git add when running pre-commit hooks

[glensc]

The original code (before this PR) breaks the intended behavior committing staged changes.

I strive for atomic commits:

• https://www.freshconsulting.com/insights/blog/atomic-commits/

so, I make changes, git add -p to stage changes for intended commit, and then do git commit. now the pre-commit hook will override my git add -p staging adding all modified files to commit.

this is unexpected and even hidden, so wouldn't even know something override my staging.

combining lint-staged update to v10, would have the best experience as it will automatically stage the changes, made in scripts ran by lint staged:

• https://github.com/okonet/lint-staged#v10

[orta]

Yeah, this seems reasonable to me 👍🏻