Update to commonmark 0.31.2

[Domeshow]

Update to commonmark 0.31.2

Please check if the PR fulfills these requirements

• It's the right issue type on the title
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
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• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)
• It does not introduce a breaking change or has a description of the breaking change

Description

Hi!

This PR ensures that the latest CommonMark spec (0.31.2) makes its way into this library.

Thanks!