Updating trunk VERSION from 4038.0 to 4039.0

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

Change-Id: Id6ca54ac5f0ec1ae9e6f5314033692d6e7a79eef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2021542Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#735215}

chrome/VERSION

 MAJOR=81
 MINOR=0
-BUILD=4038
+BUILD=4039
 PATCH=0