Updating trunk VERSION from 3963.0 to 3964.0

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

Change-Id: Idc75da0324ae551f014054afc8f03ca03c245cfb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1903689Reviewed-by: Chrome Release Bot (LUCI) <chrome-official-brancher@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#713733}

chrome/VERSION

 MAJOR=80
 MINOR=0
-BUILD=3963
+BUILD=3964
 PATCH=0