Change db host/port to rethinkdb defaults

Really cool example app! Thanks for putting it together. I tried running it after I got rethinkdb installed, and it worked until the app needed to hit the database, at which point it crashed. Took me a second to realize I needed to switch db settings in /lib to the defaults of rethinkdb. For an example app, seems like a good idea to adhere to the host/port settings rethinkdb has out of the box.

Hope this is helpful feedback!