Here’s how to run a gitbook in gitlab pages:

1. Create a repo in Gitlab
2. Clone the template here
3. Add the following file as .gitlab-ci.yml and push to gitlab:

# requiring the environment of NodeJS 6.12.x
image: node:6.12

# add 'node_modules' to cache for speeding up builds
cache:
  paths:
    - node_modules/ # Node modules and dependencies

before_script:
  - npm install gitbook-cli -g # install gitbook
  - gitbook fetch latest # fetch latest stable version
  - gitbook install # add any requested plugins in book.json

# the 'pages' job will deploy and build your site to the 'public' path
pages:
  stage: deploy
  script:
    - gitbook build . public # build to public path
  artifacts:
    paths:
      - public
  only:
    - master # this job will affect only the 'master' branch

Once you push this, you’ll have a gitbook running.