Fix gitlab ci syntax (tags, not tag)

.gitlab-ci.yml

@@ -14,7 +14,7 @@ publish-helm-chart:
     - "upload_filename=$(helm package . | sed 's/^Successfully packaged chart and saved it to: \\(.*\\)/\\1/')"
     - curl -u $HELM_CHART_REPOSITORY_CREDENTIALS -v -X POST https://charts-public.hub.eox.at/api/charts --data-binary "@${upload_filename}"
   only:
-    - tag
+    - tags
 
 
 generate-docker-compose-configs: