start.sh: exit when any of the background processes quit

This will terminate the docker container when any of the processes
(pdns_server or inotifywait) fails.

start.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 /usr/sbin/pdns_server --guardian=no --daemon=no --disable-syslog --log-timestamp=no --write-pid=no &
 
@@ -8,4 +8,8 @@ inotifywait -mqre modify --exclude '\.git' --format '%w%f' "/var/lib/powerdns/zo
         echo [$0] A modification was detected in $path
         echo [$0] Executing \`/usr/bin/pdns_control bind-reload-now $zone\`
         /usr/bin/pdns_control bind-reload-now $zone
-    done
+    done &
+
+wait -n
+
+exit $?