Fixed typos in javascript embedding code.

There were a few typos in the javascript embed code snippet (admin/help/_code.txt) which were causing the embedded snippet not to work. This fixes them:

* The `container` and `site_key` were being rendered in the code snippet via erb without using `raw` or `.html_safe`, so single quotes around the keys were actually showing as `&#x27;`.
* The default `topic_key` was being generated by `location.path`, which was `undefined` on all pages where the embed code was used, because the correct property is `location.pathname`.