update incubator chart url in aether helm charts

Change-Id: Id289b1bbe12ca4c1a190cd19f7fc16db4f29eceb
diff --git a/monitoring/grafana-aether/requirements.yaml b/monitoring/grafana-aether/requirements.yaml
index e10bc60..297a8f7 100644
--- a/monitoring/grafana-aether/requirements.yaml
+++ b/monitoring/grafana-aether/requirements.yaml
@@ -4,5 +4,5 @@
 dependencies:
   - name: grafana
     version: 5.5.0
-    repository: https://kubernetes-charts.storage.googleapis.com/
+    repository: https://charts.helm.sh/stable
     condition: grafana.enabled