Update dependency reveal.js to v4.2.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
reveal.js (source)	4.2.0 -> 4.2.1

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Release Notes

hakimel/reveal.js

v4.2.1

Compare Source

Bug fix release 🐛

Fixes

• Fix an issue where some slides disappeared (fully or partially) after slide transitions in Chrome (9e583b8 @​hakimel)
• Fix an issue that caused double-navigations and impacted presentation performance (@​hakimel #​3079)
• Fix --host not working in npm start -- --host=0.0.0.0 (@​cashcat #​3075)
• Fix incorrect sizing of auto-sized text in PDF exports (Printing With r-fit-text Too Big hakimel/reveal.js#2865 (comment) @​hakimel)
• Fix background video playback issue in some browsers by inferring MIME type from file extension (#​3078 @​vanch3d)

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