Updating trunk VERSION from 3966.0 to 3967.0

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

Change-Id: I2f5e0f4a3e6b3f530c8ff9a287656f0067ec6bb3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1912892Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#714818}

chrome/VERSION

 MAJOR=80
 MINOR=0
-BUILD=3966
+BUILD=3967
 PATCH=0