change variable names

docker-compose.yml

@@ -7,8 +7,8 @@ services:
     image: registry.bitdeals.org/certbot
     restart: unless-stopped
     environment:
-      - DOMAIN=
-      - EMAIL= # optional for notifications
+      - CERTBOT_DOMAIN=
+      - CERTBOT_EMAIL= # optional for notifications
     volumes:
       - certificates:/etc/certificates
       - letsencrypt:/etc/letsencrypt