appveyor: don't block on interactive prompts during cinst
appveyor: don't block on interactive prompts during cinst

Refs: https://github.com/facebook/watchman/pull/325

Closes: https://github.com/facebook/watchman/pull/328

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