Ignore flake8 warning about whitespace before ':' (#15663)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15663
Ignore sometimes incorrect flake8 warning about whitespace before ':'
See https://github.com/ambv/black/issues/315
Reviewed By: soumith
Differential Revision: D13565818
fbshipit-source-id: 9d5ec2335899527ee71f4b505c00865a354e3bf0
