Package check result: NOTE

Check: CRAN incoming feasibility, Result: NOTE
  Maintainer: ‘Martin R. Smith <martin.smith@durham.ac.uk>’
  
  Found the following (possibly) invalid URLs:
    URL: https://www.princeton.edu/~otorres/RStudio101.pdf
      From: inst/doc/filesystem-navigation.html
      Status: Error
      Message: SSL peer certificate or SSH remote key was not OK [www.princeton.edu]:
        SSL certificate verification failed: certificate signer not trusted. (CAfile: /etc/ssl/certs/ca-certificates.crt CRLfile: none)

Changes to worse in reverse depends:

Package: TreeDist
Check: whether package can be installed
New result: ERROR
  Installation failed.