Fedora Atomic Host comes bundled with a version of Docker based on this project atomic repo that moves no faster than the upstream kubernetes project can abide. This means that Fedora Atomic pretty much always ships with an older version of docker than what's available from Docker Inc.
However, through the magic of rpm-ostree package layering, you can replace that older, baked-in docker with the very latest docker-ce. Here's how:
First, grab the repo file for docker-ce.
# cd /etc/yum.repos.d/
# curl -O https://download.docker.com/linux/fedora/docker-ce.repo