Similar to #341 unknown certificate failure

[muschellij2]

Similar to #341, Getting this ERROR "unknown certificate failure" on Windows on @cran https://www.r-project.org/nosvn/R.check/r-release-windows-ix86+x86_64/spm12r-00check.html. Confirmed in WinBuilder: 00check.log. I've only seen this problem come up in Windows side as rest of https://cran.r-project.org/web/checks/check_results_spm12r.html have no ERRORs (Warnings are different)

Trying on @r-hub now and will post results.

Steps to Reproduce

This can be tested only on Windows, which I don't have. But Appveyor: https://ci.appveyor.com/project/muschellij2/spm12r indicates it works fine on 3.5.2-patched.

install_dir = tempdir()
    out_path = file.path(install_dir, "spm12")
    git2r::clone(
      "https://github.com/muschellij2/spm12r", 
      branch = "gh-pages", 
      local_path = out_path,
      progress = TRUE
    )