[gclient hooks] add .bat to vpython on windows
[gclient hooks] add .bat to vpython on windows

Bug: 781430
Change-Id: Idcba016f78078aa9678b8a246e964b3dcb09a016
Reviewed-on: https://chromium-review.googlesource.com/762389
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools