Updating trunk VERSION from 3959.0 to 3960.0

# This is an automated release commit.
# Do not revert without consulting chrome-pmo@google.com.
NOAUTOREVERT=true
TBR=cmasso@chromium.org

Change-Id: Id375876c2d44e0a2cddf6231b7b3f9b76857e10b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894702Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#712043}

chrome/VERSION

 MAJOR=80
 MINOR=0
-BUILD=3959
+BUILD=3960
 PATCH=0