add missing -f in front of dockerfile path

.gitlab-ci.yml

@@ -16,5 +16,5 @@ build-docker:
         tag=":$CI_COMMIT_REF_SLUG"
       fi
       echo "Running on branch '$CI_COMMIT_BRANCH': tag = $tag"
-    - docker build --pull -t "$CI_REGISTRY_IMAGE${tag}" docker/Dockerfile .
+    - docker build --pull -t "$CI_REGISTRY_IMAGE${tag}" -f docker/Dockerfile .
     - docker push "$CI_REGISTRY_IMAGE${tag}"