respondto.it doesn't return JSON and XML response

respondto.it doesn't return JSON and XML response correctly when you send a request with "application/json" in its accept field of http header, like

```
$ curl -v -H "Accept: application/json" http://respondto.it/test
Howdy
```

I don't know either if "==" is redefined in somewhere or if this is an issue regarding to sinatra, but at least it's not working for the moment without these changes.