Merge pull request #175 from philrwebb/fix_db-data_volume_path

The volume path for db-data was wrong.   needed data sub-folder.   Without that wasn't persisting the db on stop of container.

docker-compose.example.yml

@@ -25,7 +25,7 @@ services:
     image: docker.io/postgres:10-alpine
     restart: always
     volumes:
-      - db-data:/var/lib/postgresql
+      - db-data:/var/lib/postgresql/data
     environment:
       - POSTGRES_USER=limesurvey
       - POSTGRES_DB=limesurvey