Update .gitlab-ci.yml file

.gitlab-ci.yml

@@ -30,7 +30,7 @@ build-docker-image:
   services:
     - docker:dind
   before_script:
-    - echo "$DOCKER_PW" | docker login -u "$DOCKER_USER" --password-stdin "$DOCKER_REPO"
+    - echo "$DOCKER_PW" | docker login --username "$DOCKER_USER" --password-stdin "$DOCKER_REPO"
   script:
     - docker build -t "$DOCKER_REPO/$PROJECT:$CI_COMMIT_REF_SLUG" .
     - docker push "$DOCKER_REPO/$PROJECT:$CI_COMMIT_REF_SLUG"