Avoid ruining git blame

Summary:
Pure style changes can be ignored as Git 2.23 introduced
an option to ignore the hashes in a revisions file:

$ git config blame.ignoreRevsFile .git-blame-ignore-revs

This is a follow-up for e2d2390e0720.

Test Plan: git blame _modules/forest.py

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2553