chore: update download links in the README
chore: update download links in the README

w3c/epubcheck,w3c/epubcheck,IDPF/epubcheck,IDPF/epubcheck,IDPF/epubcheck,mihailim/epubcheck,IDPF/epubcheck,mihailim/epubcheck,mihailim/epubcheck,mihailim/epubcheck,mihailim/epubcheck,IDPF/epubcheck,w3c/epubcheck