YAML structure fix, postgres version fix

The structure of the environment was incorrect. The postgres dialect doesn't match the postgres:latest image.

docker-compose-postgres.yml

@@ -26,9 +26,8 @@ services:
       - spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQL94Dialect
     ports:
       - "9090:9090"
-  db:
-    container_name: webgoat_db
-    image: postgres:latest
+  webgoat_db:
+    image: postgres:9.4
 # Uncomment to store the state of the database on the host.
 #    volumes:
 #      - ./database:/var/lib/postgresql