Enable javascript so source 'show' links work in documentation.

Thank you for creating this docset, one thing I found missing was the ability to click the "show" link attached to every method for the code to be displayed. This commit enables javascript in the docset so that these links work, the change is based on instructions found at http://kapeli.com/docsets#enableJavascript.

I haven't packaged up a new version as a part of this commit, but I did create one on [this branch](https://github.com/mhaylock/rails-2.3-docset/tree/javascript_enabled) to verify that this modification does work.