Add .gitlab-ci.yml file.

Added gitlab.ci file to allow pages

.gitlab-ci.yml

+# requiring the environment of NodeJS 10
+image: node:10
+
+# 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 3.2.3 # fetch final 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
+    expire_in: 1 week
+  only:
+    - master # this job will affect only the 'master' branch