Update Grafana to 6.7.1

The most interesting new features are:
- proper limits for queried logs
- query history for logs (still a beta feature)

Change-Id: Ibd8b76b0e1e16d4bd3c74382fa3fd5a24c1bba45
diff --git a/charts/grafana/grafana.yaml b/charts/grafana/grafana.yaml
index d9bee2a..e48033e 100644
--- a/charts/grafana/grafana.yaml
+++ b/charts/grafana/grafana.yaml
@@ -52,7 +52,7 @@
 
 image:
   repository: grafana/grafana
-  tag: 6.6.2
+  tag: 6.7.1
   pullPolicy: IfNotPresent
 
   ## Optionally specify an array of imagePullSecrets.