Release volcalc 2.2.0

[Aariq]

GitHub release:

• [x] git pull
• [x] usethis::use_github_links()
• [x] urlchecker::url_check()
• [x] devtools::check(remote = TRUE, manual = TRUE)
• [ ] rhub::rhub_check(platform = "windows")
• [x] run vignettes/precompute.R script to precompute KEGG vignette
• [ ] Increment version in CITATION.cff
• [ ] usethis::use_version('minor')
• [ ] devtools::build_readme() (updates citation in README)
• [ ] usethis::use_github_release()
• [ ] usethis::use_dev_version(push = TRUE)

[Aariq]

rhub_check() fails on Windows because RCurl fails to build from source due to an RCurl error: https://cran.r-project.org/web/checks/check_results_RCurl.html.

[Aariq]

And now macOS checks fail because of issues building ChemmineOB: https://github.com/girke-lab/ChemmineOB/issues/35

[Aariq]

The CRAN issues with Rcurl appear to be fixed now: https://cran.r-project.org/web/checks/check_results_RCurl.html

[Aariq]

How to install system dependencies (open babel) with rhub?