Bump jekyll to v3.9.0, kramdown to v2.3.0

[hubot]

Release: https://github.com/jekyll/jekyll/releases/tag/v3.9.0
Diff: jekyll/jekyll@v3.8.7...v3.9.0

[ashmaroli]

Shouldn't GHP whitelist the remaining kramdown extensions so that users can opt-in to use them if needed?
In the current state, a user using, say the Coderay highlighter from kramdown v1 will suddenly have lost their code highlighting and will further not be able to load the kramdown-syntax-coderay gem to resolve the issue either.

[parkr]

Shouldn't GHP whitelist the remaining kramdown extensions so that users can opt-in to use them if needed?
In the current state, a user using, say the Coderay highlighter from kramdown v1 will suddenly have lost their code highlighting and will further not be able to load the kramdown-syntax-coderay gem to resolve the issue either.

I'm not sure that's true. The PLUGIN_WHITELIST variable is passed into Jekyll as the whitelist config entry. This is only used in the PluginManager. Since the KramdownParser code does the require-ing itself, the gems do not need to be part of this whitelist variable.

[ashmaroli]

I see. Thanks for clearing it for me. 👍

[ashmaroli]

One more question: What if a user would like to continue using kramdown v1 on GitHub Pages?

[parkr]

What if a user would like to continue using kramdown v1 on GitHub Pages?

Since we strictly version everything here, that won't be possible. If a user would like to build their site using other versions, they are welcome to use GitHub Actions!

[parkr]

This PR updates Math output from <script type='math/tex; mode=display'> to \[ ... \]. Please make sure your JavaScript library is updated to support \[ ... \].

For context: gettalong/kramdown#626 gettalong/kramdown#651