GitLab

* [ci] add CMake + R 3.6 test back (fixes #3469)

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* Update .ci/test_r_package_windows.ps1

* -Wait and remove rtools40

* empty commit
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>