[fix] return true if path not found in router

In [this line](https://github.com/flatiron/flatiron/blob/master/lib/flatiron/plugins/http.js#L81) flatiron checks if the `dispatch()` method returns true, if it doesn't then it didn't find a route and will emit `next`.

As I understand, the not found 404 route is handled by director, and if that's the case then the `dispatch()` method should return true otherwise the next [middleware in union](https://github.com/flatiron/union/blob/master/lib/routing-stream.js#L97) will be called.