Problem when use GitHub Flavored Markdown 1.0

[vmassol]

Indeed this extensions requires XWiki 12.10.7+ or 13.3+

See https://extensions.xwiki.org/xwiki/bin/view/Extension/MarkdownSyntax/GitHub-Flavored%20Markdown%20Syntax%201.0/ and Markdown Extension v8.7 Released

Thanks