composer/library/docker-traefik#3 Simplify network handling

templates/docker-compose.yml.twig

-version: '2'
+version: '3'
 
 services:
   mariadb:
@@ -204,3 +204,8 @@ services:
     volumes:
       - files:/mnt/files
 {% endif %}
+
+networks:
+  default:
+    external:
+      name: traefik_{{ projectname }}