feat(router): Support for WebSockets

WebSockets are now enabled for all new apps on Heroku. https://devcenter.heroku.com/articles/websockets#enabling-websockets

This PR does the same. Fixes #1061

To test:
```bash
git clone https://github.com/heroku-examples/ruby-ws-test.git
cd ruby-ws-test
deis create
git push deis master
deis open
```