add gitlab ci

.gitlab-ci.yml

+image: docker:latest
+services: 
+  - docker:dind
+
+build:
+  stage: build
+  script:
+    - docker login -u "gitlab-ci-token" -p "$CI_BUILD_TOKEN" $CI_REGISTRY
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA --tag $CI_REGISTRY_IMAGE:latest .
+
+deploy:
+   stage: deploy
+   script:
+    - docker login -u "gitlab-ci-token" -p "$CI_BUILD_TOKEN" $CI_REGISTRY
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    - docker push $CI_REGISTRY_IMAGE:latest
+   only:
+    - master