move cluster maintenance window

To avoid GMT/BST issues, move the maintenance window from 4-8AM UTC to
2-6AM UTC.

Google requires that the window be at least 4 hours.

Closes #11

main.tf

@@ -75,12 +75,10 @@ resource "google_container_cluster" "cluster" {
     ]
   }
 
-  # Stop Google from upgrading cluster nodes during the work week
+  # Stop Google from upgrading cluster nodes during work hours.
   maintenance_policy {
-    recurring_window {
-      recurrence = "FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR,SA,SU"
-      end_time   = "2020-01-28T08:00:00Z"
-      start_time = "2020-01-28T04:00:00Z"
+    daily_maintenance_window {
+      start_time = "02:00"
     }
   }
 }