R-devel-el-capitan-signed.pkg fails to download when testing on R devel

[jeroen]

I recommend you only test r-devel in linux, and use r-release or r-oldrel on macos. CRAN doesn’t publish OSX binary packages for r-devel: https://cran.r-project.org/bin/macosx/el-capitan/contrib/r-devel/