## Test environments
* Travis: Ubuntu Xenial (devel, release, and old-release)
* Travis: MacOS 10.13.6 (devel, release, and old-release)
* win-builder (devel, release, and old-release)
* R-hub: Solaris (32-bit, R 4.0.2), CentOS (64-bit, R 3.5.2), Fedora (gcc, R devel 2020-08-30 r79091)

## R CMD check results
There were no ERRORs or WARNINGs or NOTEs.