linkTarget in docs doesn't run for all links

[andyfleming]

Steps to reproduce:

1. Open the app ui
2. Go to the changelog in the docs section
3. Observe that some links are modified to have target="blank" like <a target="_blank" href="https://keepachangelog.com/en/1.0.0/">Keep a Changelog</a>, but some aren't like <a href="https://github.com/andyfleming/jetpax/compare/v0.2.1...v0.3.0">0.3.0</a>.

Additional Notes

This might be caused by the footnote style of links.

Existing logic in Doc.tsx:

<ReactMarkdown
    source={markdown}
    escapeHtml={false}
    linkTarget={(url) => {
        return (url.startsWith('/')) ? '' : '_blank'
    }}
/>