Release version 3.0.0, which transition to the new runtime implementation.
It shims between docker and runc instead of shipping its own runc. This allows us to decouple ourselves from Docker.
Hence new Docker release won't require new nvidia-docker2 packages.
This is tied to the version of nvidia-docker 2.1.0: https://github.com/NVIDIA/nvidia-docker/releases/tag/v2.1.0