minor: delete useless environment variable

MongoDB is fundamentally designed for "create on first use", so if you do not insert data with your JavaScript files, then no database is created.

Author: jinrenjie

docker-compose.yaml

@@ -22,7 +22,6 @@ services:
     environment:
       - MONGO_INITDB_ROOT_USERNAME=$DB_USER
       - MONGO_INITDB_ROOT_PASSWORD=$DB_PASS
-      - MONGO_INITDB_DATABASE=$DB_NAME
     ports:
       - "$DB_PORT:$DB_PORT"
     volumes: