Merge pull request #2457 from jupyterhub/update-chart-prometheus

Updates prometheus chart to 19.3.3

Author: minrk

mybinder/Chart.yaml

@@ -31,7 +31,7 @@ dependencies:
   #       chart v11.16.9 maps to app v2.21.0  - 2020-12-06
   #       chart v12 requires Helm 3
   - name: prometheus
-    version: "18.2.0"
+    version: "19.3.3"
     repository: https://prometheus-community.github.io/helm-charts
     condition: prometheus.enabled