Setup CI

.gitlab-ci.yml

+before_script:
+  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
+build-master:
+  script:
+    - docker build --pull -t $CI_REGISTRY_IMAGE/maven ./docker
+    - docker push $CI_REGISTRY_IMAGE/maven
+  only:
+    - master