Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Building Heroku-based application using gliderlabs/herokuish docker image...
Cannot connect to the Docker daemon at tcp://localhost:2375. Is the docker daemon running?
Cannot connect to the Docker daemon at tcp://localhost:2375. Is the docker daemon running?
time="2019-12-26T22:15:14Z" level=error msg="failed to dial gRPC: cannot connect to the Docker daemon. Is 'docker daemon' running on this host?: dial tcp 127.0.0.1:2375: connect: connection refused"
Cannot connect to the Docker daemon at tcp://localhost:2375. Is the docker daemon running?
section_end:1577398514:build_script
section_start:1577398514:after_script
section_end:1577398514:after_script
section_start:1577398514:upload_artifacts_on_failure
section_end:1577398514:upload_artifacts_on_failure
ERROR: Job failed: command terminated with exit code 1