check_win returns curl error

[brpetrucci]

I've been testing my package with check_win_devel() and check_win_release() for the past week, and even submitted one check today successfully. The check results never arrived on my e-mail, though, and now when trying to run them again I get an error

> devtools::check_win_release("~/Packages/paleobuddy")
Building windows version of paleobuddy (0.0.0.900) for R-release with win-builder.r-project.org.
...
Error in curl::curl_fetch_memory(url, handle = h) : 
  Failed FTP upload: 550

I'm assuming this is a win_builder() problem, since both devtools::check() and Travis-CI are working with my package. In issue #1435 it seemed like it was solved after some time, but wanted to bring it to your attention that the same issue is turning up again.

[jimhester]

This is an upstream issue with CRAN's build machines, likely it should resolve itself soonish.