This improves output from ninja a bit on Windows when
NINJA_SUMMARIZE_BUILD is set.

The trailing space was removed in https://crrev.com/c/3400399.

Change-Id: Ifb14129a436a2673969f529d0c9143118dd87d6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3833272
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>