chore(docker): update volume mappings for development environment

docker-compose.override.yml

@@ -6,7 +6,8 @@ services:
       dockerfile: Dockerfile.dev
     volumes:
       - .:/app
-      - /app/vendor        # keeps vendor from the dev image, not your local dir
+      - ./vendor:/app/vendor
+      - /app/var/data
     environment:
       APP_ENV: dev
       APP_DEBUG: "1"