docs: update Travis logo URL
docs: update Travis logo URL
mihailim/epubcheck,mihailim/epubcheck,mihailim/epubcheck,IDPF/epubcheck,mihailim/epubcheck,IDPF/epubcheck,IDPF/epubcheck,w3c/epubcheck,IDPF/epubcheck,mihailim/epubcheck,w3c/epubcheck,IDPF/epubcheck,w3c/epubcheck