Filter out deleted paths from files_to_lint in the pre-push hook (#38)
Filter out deleted paths from files_to_lint in the pre-push hook (#38)

## Summary:
I'm a little wary about changing this as I have never personally used it (I deleted all git hooks shortly after cloning webapp the first time),
but this feels like a minimally invasive change.

Issue: https://khanacademy.atlassian.net/browse/FEI-3574

## Test plan:
🤞

Author: jaredly

Reviewers: kevinbarabash, somewhatabstract

Required Reviewers: 

Approved by: kevinbarabash, somewhatabstract

Checks: 

Pull request URL: https://github.com/Khan/khan-linter/pull/38

Khan/khan-linter,Khan/khan-linter,Khan/khan-linter,Khan/khan-linter