Fix issues with creating orphan processes

By using bash (which plays nicely by reparenting orphan processes)

update-dns.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 set -eux
 
@@ -28,3 +28,5 @@ EOM
 )
 
 aws route53 change-resource-record-sets --hosted-zone-id "${zone_id}" --change-batch "$batch"
+
+wait