`docker login -p` throws an error

[psgivens]

invoicer-chapter3/.circleci/config.yml

Line 60 in 37da2ca

docker login -u ${DOCKER_USER} -p ${DOCKER_PASS};

It looks like docker depricated the use of the -p flag. Changing the line to the following fixed it for me.
echo ${DOCKER_PASS} | docker login -u ${DOCKER_USER} --password-stdin;