Format with black 18.9b0
Format with black 18.9b0

Summary: Reformat all opted-in python code with version `18.9b0` of Black.

Reviewed By: ambv

Differential Revision: D10126605

fbshipit-source-id: 82af0d645dd411ce8ae6b8d239e151b3730cd789

nodakai/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,facebook/watchman,wez/watchman,facebook/watchman,facebook/watchman,wez/watchman,facebook/watchman,wez/watchman,wez/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,facebook/watchman