[pkg] opt into autoformat
Summary: woooo
Test Plan: arc lint --apply-patches --take BLACK --paths-cmd 'hg files -I "caffe2/**/*.py"'
Reviewed By: SplitInfinity
Differential Revision: D28608934
fbshipit-source-id: 7768fed50a87883a95319376c0a6d73a9492bdcc
