CircleCI: Specify remote docker image
CircleCI: Specify remote docker image

CircleCI is deprecating older machine images. This includes the image
docker-17.09.0-ce image, which is the default for the
"setup_remote_docker" step. Replace it with 19.03.13, the latest
available docker version.

mozilla/ichnaea,mozilla/ichnaea,mozilla/ichnaea,mozilla/ichnaea