Set up CI to publish the demo HTML

[asokolsky]

Neither of these works:
http://jacebrowning.github.io/doorstop-demo
https://travis-ci.org/jacebrowning/doorstop-demo

[jacebrowning]

Thanks! The demo HTML is here: http://doorstop-dev.github.io/demo/

Someone will have to set up CI for this project to get it rebuilding automatically.