Updating trunk VERSION from 4030.0 to 4031.0

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

Change-Id: I20fc48c994e76947027296a5469b3bac7f71bcae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2005863Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#732703}

chrome/VERSION

 MAJOR=81
 MINOR=0
-BUILD=4030
+BUILD=4031
 PATCH=0