Update .gitlab-ci.yml file

  before_script:

    - pip install -q mkdocs-material mike

    - apt-get update -qq && apt-get -qq install -y git > /dev/null

    - git config --global --replace-all user.name $GITLAB_USER_NAME

    - git config --global --replace-all user.email $GITLAB_USER_EMAIL

    - git config --global user.email "${GITLAB_USER_EMAIL}"

    - git config --global user.name "${GITLAB_USER_NAME}"

    - git fetch origin $PAGES_BRANCH && git checkout $PAGES_BRANCH || git checkout -b $PAGES_BRANCH origin/$PAGES_BRANCH || echo "Pages branch not deployed yet."

    - git checkout $CI_COMMIT_SHA

  script: