Update sessionConfig with missing cookie attribute

This PR updates the Sessions example with actually working code. 

I've added the `cookie` attribute to the `sessionConfig` because it's mandatory at the moment (see [bone.io middleware](https://github.com/techpines/bone.io/blob/master/lib/node/middleware.coffee)) and I've also fixed a syntax error when setting up the session middleware.

Thanks for bone.io. Looks interesting even tho I've only played around with it a little.