Lock version of Org Ruby to 0.9.7

Currently the version being used at Github is 0.9.1. By updating to 0.9.7 the following issues would be addressed:

 - Fix Org mode syntax for escaping html: Syntax actually now is `@@html:<text>@@`
 - Fix `#+TITLE:` to render as a h1 headline
   https://github.com/github/markup/issues/309
 - Remove rewriting links to '.org' files as '.html'
   https://github.com/github/markup/issues/100   
 - Implement :exports options for code blocks
 - Fix code blocks prepended comma stripping
 - Bugfix: Recognize `#+RESULTS:` block from named blocks

Cheers!