Update .gitlab-ci.yml file

.gitlab-ci.yml

+image: docker:19.03.1
+
+stages:
+- build
+- test
+
+before_script:
+- docker login -u ${CI_REGISTRY_USER} -p ${CI_REGISTRY_PASSWORD} ${CI_REGISTRY}
+
+build:
+  stage: build
+  script:
+  - docker pull ${CI_REGISTRY_IMAGE}:latest || true
+  - docker build --cache-from ${CI_REGISTRY_IMAGE}:latest
+                 --tag ${CI_REGISTRY_IMAGE}:${CI_COMMIT_REF_SLUG}
+                 --tag ${CI_REGISTRY_IMAGE}:latest .
+  - docker push ${CI_REGISTRY_IMAGE}:${CI_COMMIT_REF_SLUG}
+  - docker push ${CI_REGISTRY_IMAGE}:latest
+  only:
+  - master
+
+test:
+  stage: test
+  script:
+  - mkdir out
+  - docker run --name examscan --rm -v $(pwd):$(pwd) -w $(pwd) ${CI_REGISTRY_IMAGE}:latest watermark.py --i pdfs --o out
+  artifacts:
+    paths:
+    - out/