Fix syntax

docker/mariadb/docker-compose.yaml

@@ -1,4 +1,6 @@
-mariadb:
+version: "3"
+services:
+  mariadb:
     container_name: mariadb
     image: mariadb
     environment:
@@ -11,6 +13,6 @@ mariadb:
       - /etc/localtime:/etc/localtime:ro
     restart: always
 
-networks:
+  networks:
     db:
       external: true