Hugo 0.62.1: A couple of Bug Fixes

This release is mainly motivated by getting this demo site up and running. It demonstrates truly portable Markdown links and images, whether browsed on GitHub or deployed as a Hugo site.

• Support files in content mounts ff6253bc @bep #6684#6696
• Update alpine base image in Dockerfile to 3.11 aa4ccb8a @RemcodM
• hugolib: Fix inline shortcode regression 5509954c @bep #6677