remove example.env from docker-compose file to avoid confusion

Author: gerrykou

bootcamp/materials/1-dimensional-data-modeling/docker-compose.yml

@@ -5,7 +5,6 @@ services:
     container_name: ${DOCKER_CONTAINER}
     env_file:
       - .env
-      - example.env
     environment:
       - POSTGRES_DB=${POSTGRES_SCHEMA}
       - POSTGRES_USER=${POSTGRES_USER}