Point to the Rouge GitHub repo rather than broken website (#9362)

Merge pull request 9362

docs/_docs/liquid/tags.md

@@ -15,7 +15,7 @@ If you have page snippets that you use repeatedly across your site, an
 ## Code snippet highlighting
 
 Jekyll has built in support for syntax highlighting of over 100 languages
-thanks to [Rouge](http://rouge.jneen.net). Rouge is the default highlighter
+thanks to [Rouge](https://github.com/rouge-ruby/rouge). Rouge is the default highlighter
 in Jekyll 3 and above.
 
 {: .note .warning}

docs/_docs/upgrading/2-to-3.md

@@ -89,7 +89,7 @@ then the layout can access that via {% raw %}`{{ layout.class }}`{% endraw %}.
 
 For the first time, the default syntax highlighter has changed for the
 `highlight` tag and for backtick code blocks. Instead of [Pygments.rb](https://github.com/tmm1/pygments.rb),
-it's now [Rouge](http://rouge.jneen.net/). If you were using the `highlight` tag with certain
+it's now [Rouge](https://github.com/rouge-ruby/rouge). If you were using the `highlight` tag with certain
 options, such as `hl_lines`, they may not be available when using Rouge. To
 go back to using Pygments, set `highlighter: pygments` in your
 `_config.yml` file and run `gem install pygments.rb` or add