Release: r-buildpack (06-27)

[cf-buildpacks-eng]

Release reminder for r-buildpack

The ideal release date window for this buildpack starts on: 06-27 and ends on 07-02.

• See diff from latest version and validate if a release is required.
• Make sure the latest commit on has passed tests on the CI
• Refer release instructions. (private link)

[arjun024]

-> #298