Package check result: NOTE

Check: CRAN incoming feasibility, Result: NOTE
  Maintainer: ‘Shixiang Wang <w_shixiang@163.com>’
  
  Found the following (possibly) invalid URLs:
    URL: https://xena.treehouse.gi.ucsc.edu:443/
      From: inst/doc/USCSXenaTools.html
            README.md
      Status: Error
      Message: SSL peer certificate or SSH remote key was not OK [xena.treehouse.gi.ucsc.edu]:
        server verification failed: certificate signer not trusted. (CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none)

No changes to worse in reverse depends.