Add missing import for saltURL in bin.js

@dasmoth 

There seems to be a unresolved `saltURL` variable in `bin.js`, which seems to be solved by importing it from `utils`.

Discovered this when I was trying a Trix-based gene search on a Safari, which triggered an exception:

![screen shot 2014-08-25 at 6 22 07 pm](https://cloud.githubusercontent.com/assets/7988161/4038899/b7b375c0-2cbf-11e4-9e1c-424f7e0ecfad.png)