refactor: update markdown to 3.8 and adapt extension code for compatibility#303

UsamaSadiq merged 1 commit intoopenedx:edx_releaseopenedx/django-wiki:edx_releasefrom

wgu-ram-chandra:fix-markdown-compatibilitywgu-ram-chandra/django-wiki:fix-markdown-compatibilityCopy head branch name to clipboard