cmd/gerritbot: up RAM limits in k8s config

Change-Id: I0939e245f8dd2573e099491e0e014dc8571b6ebe
Reviewed-on: https://go-review.googlesource.com/127676
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: andybons

cmd/gerritbot/deployment-prod.yaml

@@ -23,6 +23,6 @@ spec:
         resources:
           requests:
             cpu: "1"
-            memory: "1Gi"
+            memory: "4Gi"
           limits:
-            memory: "2Gi"
+            memory: "6Gi"