Pre-install Docker on macOS images
Running UI tests on an iOS app often means having a "clean room" server environment to run tests against. More and more, servers are using Docker to deploy bundle and run server instances.
Unfortunately, the current macOS images don't have Docker pre-installed (even though the docs seem to indicate otherwise here: https://circleci.com/docs/2.0/docker-compose/)
This is a request to ensure Docker is pre-installed onto the macOS images so iOS tests can spin up a server instance if needed.