add missing apostrophe

.gitlab-ci.yml

@@ -58,6 +58,6 @@ publish_guide:
   script:
     - 'rsync -av angelguide_*.pdf $PUBLISH_USER@$PUBLISH_HOST:$PUBLISH_PATH'
   rules:
-    - if: '$CI_COMMIT_REF_NAME == "master"' && $CI_COMMIT_TAG != null
+    - if: '$CI_COMMIT_REF_NAME == "master" && $CI_COMMIT_TAG != null'
       when: on_success
     - when: never