message: Add link to bug
diff: export DOCKER_CONTENT_TRUST=${DOCKER_CONTENT_TRUST:-1}
  # Enable Docker BuildKit (https://docs.docker.com/develop/develop-images/build_enhancements)
  -# TODO(fortuna): Re-enable after we figure out how to make it work on Travis.
  +# TODO(fortuna): Re-enable after we figure out how to make it work on Travis: https://github.com/moby/buildkit/issues/606
  # export DOCKER_BUILDKIT=1
  docker build --force-rm --build-arg GITHUB_RELEASE="${TRAVIS_TAG:-none}" -t ${SB_IMAGE:-outline/shadowbox} $ROOT_DIR -f src/shadowbox/docker/Dockerfile
  