Revert "Remove obsolete version attribute"

This reverts commit 31ef4e62.

dev.yml

+version: "3"
+
 services:
   dolibarr:
       ports:

docker-compose.yml

+version: "3"
+
 services:
   mariadb:
       image: mariadb:latest

expose_mariadb.yml

+version: "3"
+
 services:
   mariadb:
       ports: