Please merge support for front-end proxies that listen to different ports than the app server.

Hi, thank you very much for making dropwizard-swagger it helped me get my dropwizard based project (http://psaw.osaa.dk) working with swagger much faster than I would otherwise.

I have a setup which I think is not too dissimilar from what others would use in production, where I run an nginx frontend which listens on the public interface on port 80, while the dropwizard applications listens on localhost on a completely different port.

I really like being able to firewall off access to the app server, so all access goes through nginx, so for this reason I need to tell swagger to use my port number rather than the one that dropwizard listens to.

Here's my quick fix, it just continues along the same lines as the original "set host name manually"-fix, so I hope it can be merged.