Update Gemfile.lock

[cmc333333]

I recently received this message from a gh-pages build:

The page build completed successfully, but returned the following warning:

You are attempting to use the 'pygments' highlighter, which is currently unsupported on GitHub Pages. Your site will use 'rouge' for highlighting instead. To suppress this warning, change the 'highlighter' value to 'rouge' in your '_config.yml'. For more information, see https://help.github.com/articles/page-build-failed-config-file-error/#fixing-highlighting-errors.

For information on troubleshooting Jekyll see:

https://help.github.com/articles/using-jekyll-with-pages#troubleshooting

If you have any questions you can contact us by replying to this email.

I think we need to update the pegged library versions, and, in the process, replace pygments with rouge.