https://docs.docker.com/install/linux/docker-ce/ubuntu/#install-docker-ce-1
Change "stable" repository to "edge" and works fine.
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04 LTS
Release: 18.04
Codename: bionic
$ docker --version
Docker version 18.05.0-ce, build f150324