Fixed path for the PostgreSQL data folder (#1520)

The ending `data` folder does not exist per the Postgres documentation
and causes errors when starting up the Docker Compose Stack.

docs/content/deployment/docker.mdx

@@ -54,7 +54,7 @@ services:
           POSTGRES_USER: bracket_prod
           POSTGRES_PASSWORD: bracket_prod
         volumes:
-          - ./postgres:/var/lib/postgresql/data
+          - ./postgres:/var/lib/postgresql
 ```
 
 ## 3. Set up the environment variables