R development version (3.7) does not work for Mac

I cannot run the development version of R (which will become 3.7) on macOS on Travis. The issue is similar to this one last year for R 3.5. My error is:

Installing R
287.60s$ brew update >/dev/null
==> Downloading https://homebrew.bintray.com/bottles-portable-ruby/portable-ruby-2.3.7.mavericks.bottle.tar.gz
######################################################################## 100.0%
==> Pouring portable-ruby-2.3.7.mavericks.bottle.tar.gz
3.99s$ curl -fLo /tmp/R.pkg https://r.research.att.com/el-capitan/R-devel/R-devel-el-capitan-signed.pkg
curl: (22) The requested URL returned error: 404 Not Found
The command "eval curl -fLo /tmp/R.pkg https://r.research.att.com/el-capitan/R-devel/R-devel-el-capitan-signed.pkg " failed. Retrying, 2 of 3.

I succeed in running the development version of R on Linux on Travis and get:

Rscript -e 'sessionInfo()'
R Under development (unstable) (2019-06-26 r76742)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 16.04.6 LTS

My solution was to exclude that build to pass the tests on Travis.