Another style of rainbow for multipolygons

The CartoDB office in Brooklyn is a multipolygon, so we need to specify a different ID for it (`[osm_id = -3720805], // Brooklyn`) but we also need to change the rainbow style because it breaks otherwise. Here's now the new style looks: 

![screen shot 2014-12-03 at 10 37 12 am](https://cloud.githubusercontent.com/assets/1212178/5278446/d729757c-7ad9-11e4-829a-011f2bdf8892.png)