Update URL for the “Soy” package repository.

We changed our GitHub organization username from “Obvious” to “Medium” — the old URLs still redirect, but the package control website reports the repository as missing. This fixes the URL.

![screen shot 2014-09-29 at 3 26 34 pm](https://cloud.githubusercontent.com/assets/301442/4450635/c5f51f52-4827-11e4-8916-8552dd9d60e8.png)