Maybe I don't have mattermost-dev running in docker?
I can browse mattermost in the browser but when I run docker ps it looks like I only have mysql and postgres.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
91e91261f6dc postgres:9.4 "/docker-entrypoint.s" 24 hours ago Up 22 hours 0.0.0.0:5432->5432/tcp mattermost-postgres
299a1953932e mysql:5.7 "/entrypoint.sh mysql" 24 hours ago Up 22 hours 0.0.0.0:3306->3306/tcp mattermost-mysql