Fix invalid syntax in docker-compose.yml

docker-compose.yml

@@ -19,7 +19,7 @@ services:
     image: postgres:9.6
     container_name: inventory_postgres
     ports:
-    - "5432:5432"
+      - "5432:5432"
     volumes:
       - ${PGDATA_VOLUME}:/var/lib/postgresql/data/pgdata
     environment: