Update Docker from 19.03 to 20.10 used in CI
Updates Docker daemon and CLI from 19.03 to 20.10 used in CI. Also removes DOCKER_DRIVER
variable since overlay2
has been the default storage driver (cf. Docker 18.09 release note: https://docs.docker.com/engine/release-notes/18.09/#deprecation-notices).
Closes #18 (closed)