This fixes autoninja on my Windows machine at home.

Bug: none
Change-Id: I3c245715c409bb2b30fcc3733bb097fc2a88f464
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2021755Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>