Update Docker port mapping to match both to env var

docker-compose.yml

@@ -15,7 +15,7 @@ services:
   nanodrop:
     build: .
     ports:
-      - "${PORT:-3000}:3000"
+      - "${PORT:-3000}:${PORT:-3000}"
     environment: { <<: *env }
     volumes:
       - nanodrop-data:/app/data