Update .gitlab-ci.yml

.gitlab-ci.yml

@@ -8,9 +8,9 @@ build_docker:
     retry: 2
     tags:
         - linux
-    rules:
-        - changes:
-            - docker/Dockerfile
+    only:
+        refs:
+            - master
     script:
         - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
         - docker build -f docker/Dockerfile -t $CI_REGISTRY/$CI_PROJECT_PATH:latest .