make editing the api server easier

- currently when a change is made to api-stub/routes the server has
  to be restarted. this change allows you to start the server with
  something like nodemon, e.g., npm install nodemon -g, then nodemon
  api-stub/server.js — then start the grunt task with `grunt server:proxy`

  make changes inside of the routes file and now the second server that
  we’re parodying to through will restart itself due to the fact that it
  was started with nodemon

does that make sense?

basically, you don’t have to use this feature, but if you do, run the f
following commands:

in one window: WUNDERGROUND_KEY=blah FIVEHUNDRED_PX_KEY=blah nodemon api-stub/server.js
in a second window: grunt server:proxy