set rvm_git_clone_depth
do not publish on PR [ci skip]
Merge branch 'rkh-multi-os' of https://github.com/travis-ci/travis-rubies into rkh-multi-os
Revert "with --with-gcc=gcc"

This reverts commit c35e9d1c090a44889c267560b602c842f37a52cf.
Revert "do not unset CC"

This reverts commit 30a81def2b3298583c47a8db3b7b065bed9164a8.