Fix what I believe is a typo: "Mac OS" instead of "Max OS"
Fix what I believe is a typo: "Mac OS" instead of "Max OS"

Reviewed By: wez

Differential Revision: D4412257

fbshipit-source-id: c5b33fb82492a7084125c9d5b66a240751eb5cc0

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