TT#87854 Update to latest grml2usb version 0.18.3

grml2usb v0.18.1 included a regression that caused us to revert to
grml2usb v0.17.0 in commmit 9fbc9afeda.

The according fix for our needs is
657b880f02
and was released as v0.18.2

grml2usb v0.18.3 supports Grml's new Secure Boot approach and switches
in grml2iso from isohybrid to xorriso/isohybrid to properly support EFI
boot, besides some further code cleanups, docs improvements and
bugfixes.

Change-Id: I0ce25d05825767120144315f07ded2c66bfffc0f

build_iso.sh

@@ -16,7 +16,7 @@ TEMPLATES="templates"
 GRML_URL="${GRML_URL:-https://deb.sipwise.com/deployment-iso/grml/}"
 GRML_HASH_URL="${GRML_HASH_URL:-https://deb.sipwise.com/deployment-iso/grml/}"
 SIPWISE_ISO="sip_provider_${MR}_${DATE}.iso"
-GRML2USB_VERSION='v0.17.0'
+GRML2USB_VERSION='v0.18.3'
 
 usage () {
   echo "Usage: $0 compat <grml.iso> <mr version> <Debian dist>"