Fixed mixed content warning when loading jquery without SSL

Loading https://training.github.com/kit/ results in a mixed content warning and blocks jQuery:

![screen shot 2014-06-16 at 9 36 23 am](https://cloud.githubusercontent.com/assets/1060/3284848/6a90d726-f531-11e3-9e6a-a96e49f86b30.png)

This PR uses the jquery available in `_javascripts` instead, avoid that issue entirely.

cc @jordanmccullough @matthewmccullough