Keep OSM attribution box expanded

For whatever reason, the code from [this page](http://bl.ocks.org/lxbarth/9490377) didn't work -- the attribution would repeat twice. Haven't mapbox twice isn't too bad. We can tweak in the future. cc: @tchu88 

(Note: this also required a minor bump in mapbox versions 1.6.2 -> 1.6.4)

![screen shot 2014-06-26 at 12 01 51 am](https://cloud.githubusercontent.com/assets/1435836/3392432/7327863e-fcb4-11e3-8f41-915249c572a2.png)