devtools/config: set docker-compose version to 2.4
Version 3 of the compose spec removes support
for the extends keyword.
Trust: Jamal Carvalho
Run-TryBot: Jamal Carvalho
# Use of this source code is governed by a BSD-style
# license that can be found in the LICENSE file.
-version: '3'
+version: '2.4'
services:
# nodejs is used to run npm scripts from ../../package.json. It mounts the
# pkgsite root directory into a container and obscures the git directories
