This is a re-submission to fix invalid URL. ## Test environments * local mac OS install, R 4.0.2 * ubuntu 20.04 (on github actions), R-devel, R 4.0.2, R 3.6.3, 3.5.3, R 3.4.4, R 3.3.3 * mac OS 10.15.4 (on github actions) R-devel, R 4.0.2 * Microsoft Windows Server 2019 10.0.17763 (on github actions) R 4.0.2 ## R CMD check results 0 errors v | 0 warnings v | 0 notes v R CMD check succeeded ## revdepcheck results No worsening reverse dependencies.