Update remark-sub-super for compatibility with remark >= 13

[hubgit]

remark-sub-super has not yet updated to be compatible with remark v13, which uses micromark as the parser.

• https://github.com/micromark/micromark#creating-a-micromark-extension
• https://unifiedjs.com/learn/guide/create-a-plugin/
• https://github.com/micromark/micromark#extending-markdown
• https://github.com/remarkjs/remark/pull/536
• https://github.com/remarkjs/remark/blob/main/doc/plugins.md
• https://github.com/remarkjs/remark/releases/tag/13.0.0