highlight.js 9.x is obsolete and leads to warnings when used

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> highlight.js@9.18.5 postinstall /source/node_modules/highlight.js
> node deprecated.js
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Verion 9 of Highlight.js has reached EOL. It will no longer
be supported or receive security updates in the future.
Please upgrade to version 10 or encourage your indirect
dependencies to do so.
For more info:

https://github.com/highlightjs/highlight.js/issues/2877
https://github.com/highlightjs/highlight.js/blob/master/VERSION_10_UPGRADE.md

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