build(deps-dev): bump dompurify from 2.3.10 to 2.5.6 in /docs (#726)

Bumps [dompurify](https://github.com/cure53/DOMPurify) from 2.3.10 to 2.5.6.
- [Release notes](https://github.com/cure53/DOMPurify/releases)
- [Commits](cure53/DOMPurify@2.3.10...2.5.6)

---
updated-dependencies:
- dependency-name: dompurify
  dependency-type: indirect
...

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