use tickers instead of time.After to avoid memory leak (#5220)

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/clouddns/clouddns.go

@@ -82,12 +82,16 @@ func (h *CloudDNS) Run(ctx context.Context) error {
 		return err
 	}
 	go func() {
+		delay := 1 * time.Minute
+		timer := time.NewTimer(delay)
+		defer timer.Stop()
 		for {
+			timer.Reset(delay)
 			select {
 			case <-ctx.Done():
 				log.Debugf("Breaking out of CloudDNS update loop for %v: %v", h.zoneNames, ctx.Err())
 				return
-			case <-time.After(1 * time.Minute):
+			case <-timer.C:
 				if err := h.updateZones(ctx); err != nil && ctx.Err() == nil /* Don't log error if ctx expired. */ {
 					log.Errorf("Failed to update zones %v: %v", h.zoneNames, err)
 				}