Get tests passing in v1.0

[ChrisRackauckas]

Hey @Non-Contradiction , can we get some help getting tests to pass on Julia v1.0? I'm not sure why it's saying devtools is missing now.

[Non-Contradiction]

Sue! What is the R version you are using? And what is the message?
devtools relies on Rtools, and I think there are some problems related to Rtools in R 3.5.1 or R 3.5.0 on windows.

[ChrisRackauckas]

I haven't been able to get it running locally so I am referring to our Travis and AppVeyor results:

https://travis-ci.org/JuliaDiffEq/diffeqr/jobs/462113215

[Non-Contradiction]

This failure is a "network" problem. The CRAN mirror seems to restrict connections. Whenever the package cache on Travis is invalidated, Travis needs to connect to CRAN to get packages with newer versions, and the problem occurs randomly. I also had this kind of problem sometimes, and I just restarted the build (but not too frequently) to deal with this.