update postgres volume path (#1)

docker-library/postgres#1259

Author: NeSoLeK

docker-compose.yml

@@ -8,7 +8,7 @@ services:
     ports:
       - "5432:5432"
     volumes:
-      - pg_data:/var/lib/postgresql/data
+      - pg_data:/var/lib/postgresql
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U langtutor"]
       interval: 10s