update to latest loofah HTML sanitizer

The site uses loofah to sanitize the text coming from the package descriptions, which can come from the app's source repo. This updates loofah to the latest version. To check whether there were any changes or regressions from this, I downloaded the tarballs for the previous CI build and then this CI build, then used meld to check for diffs. The only diffs were the git commit ID used in the version tag in the site footer, and an integer used in the search CSS names.