Update .gitlab-ci.yml file

.gitlab-ci.yml

+dockerize:
+  stage: build
+  tags:
+    - intro-shell
+  script:
+    - docker login -u "${CI_REGISTRY_USER}" -p "${CI_REGISTRY_PASSWORD}" "${CI_REGISTRY}"
+    - docker build -t "${CI_REGISTRY_IMAGE}" --no-cache .
+    - docker push "${CI_REGISTRY_IMAGE}"