Caching with multiple versions of R - failing new RDS

With builds using cache: packages but multiple versions of R https://travis-ci.com/neuroconductor-devel/ITKR/builds/123272821,
we have failures on jobs, such as
https://travis-ci.com/neuroconductor-devel/ITKR/jobs/225302496, but it catches
fetching 0.5.0.s/cache-osx-xcode9-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855--R-3.3.3.tgz, which seems to be an OSX, R 3.3.3 cache, but when it runs, it fails on

  cannot read workspace version 3 written by R 3.6.1; need R 3.5.0 or newer

https://travis-ci.com/neuroconductor-devel/ITKR/jobs/225302496#L3109
which I’m confused because I believe the cache should have an RDS that is R 3.3 specific.

@jeroen @jimhester

My fault - I believe it was trying to install a package that is from a future R version, not the cache. Please disregard or I’ll delete. Sorry for the inconvenience.

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