update gitlab-ci script syntax

.gitlab-ci.yml

@@ -318,7 +318,7 @@ spinach:other:ruby22:
 notify:slack:
   stage: notifications
   script:
-    - ./scripts/notify_slack.sh "#builds" "Build failed! Check https://gitlab.com/gitlab-org/$(basename „$PWD)/commit/$CI_BUILD_REF/builds"
+    - ./scripts/notify_slack.sh "#builds" "Build on \`$CI_BUILD_REF_NAME\` failed! Check https://gitlab.com/gitlab-org/$(basename "$PWD")/commit/"$CI_BUILD_REF"/builds"
   when: on_failure
   only:
     - master@gitlab-org/gitlab-ce