Caddy web server and Flash file

When I ask for a flash file like http://www.example.com/test.swf on my Caddy server (http://caddyserver.com/), browsers start to download it instead of opening it. How to set up Caddy so flash file (*.swf) could be directly opened by browser. I think I need to define Mime type on the server side in Caddyfile. What parameter should I set ? Thank you. Marcel