fixed missing MYSQL_ROOT_PASSWORD variable

docker-compose.yml

@@ -8,6 +8,8 @@ services:
        - ./data/mysql:/var/lib/mysql/
        - ./data/backup:/mnt/backup
      restart: on-failure:3
+     environment:
+       MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
 
 networks:
    db_default: