Image to run GitHub's certificationy/certificationy-cli.
Base image is php:5.5-apache.
Start a container like this:
docker run -ti danielrhodeswarp/certificationy-cli
You should now be "in" the container and can run certificationy-cli thus:
php certificationy.php --number=20
Please see https://github.com/certificationy/certificationy-cli for the gory command line details.
(Image's CMD is /bin/bash.)