Update dependency react-markdown to v4

[renovate]

This PR contains the following updates:

Package	Type	Update	Change	References
react-markdown	devDependencies	major	^3.4.1 -> ^4.0.0	source

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Release Notes

rexxars/react-markdown

v4.0.3

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Fixes

• Output paragraph element for last item in loose list (Jeremy Moseley)

v4.0.2

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Fixes

• Fix text rendering in React versions lower than or equal to 15 (Espen Hovlandsdal)

v4.0.1

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Fixes

• [TypeScript] Fix TypeScript index signature for renderers (Linus Unnebäck)

v4.0.0

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BREAKING

• text is now a first-class node + renderer - if you are using allowedNodes, it needs to be included in this list. Since it is now a React component, it will be passed an object of props instead of the old approach where a string was passed. children will contain the actual text string.
• On React >= 16.2, if no className prop is provided, a fragment will be used instead of a div. To always render a div, pass 'div' as the root renderer.
• On React >= 16.2, escaped HTML will no longer be rendered with div/span containers
• The UMD bundle now exports the component as window.ReactMarkdown instead of window.reactMarkdown

Added

• HTML parser plugin for full HTML compatibility (Espen Hovlandsdal)

Fixes

• URI transformer allows uppercase http/https URLs (Liam Kennedy)
• [TypeScript] Strongly type the keys of renderers (Linus Unnebäck)

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