Update .gitlab-ci.yml file

.gitlab-ci.yml

+variables:
+  DOCKER_TLS_CERTDIR: "/certs"
+
+docker-build:
+  stage: build
+  image: docker:cli
+  services:
+    - docker:dind
+  before_script:
+    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
+  script:
+    - docker build --pull -t "$DOCKER_IMAGE_NAME" .
+    - docker push "$DOCKER_IMAGE_NAME"
+    - |
+      if [[ "$CI_COMMIT_BRANCH" == "$CI_DEFAULT_BRANCH" ]]; then
+        docker tag "$DOCKER_IMAGE_NAME" "$CI_REGISTRY_IMAGE:latest"
+        docker push "$CI_REGISTRY_IMAGE:latest"
+      fi
+  rules:
+    - if: $CI_COMMIT_BRANCH
+      exists:
+        - Dockerfile
\ No newline at end of file