industrial_ci: gitlab example code fails on gitlab with shell executor

I tried using the example .gitlab-ci.yml from the README.md and it is failing due to apk missing:

bash: line 90: apk: command not found

Here is my config (copied from README.md):

image: docker:git
services:
  - docker:dind
before_script:
  - apk add --update bash coreutils tar
  - git clone --quiet --depth 1 https://github.com/ros-industrial/industrial_ci .industrial_ci
melodic:
  script: .industrial_ci/gitlab.sh ROS_DISTRO=melodic