d/rules: Declare that we have grub >= 2.02

Debian's grub packaging runs grub-install in postinst, so we should be
able to rely on grub actually getting updated.

debian/rules

@@ -20,6 +20,7 @@ configure_options = \
 	--with-libarchive \
 	--with-libsystemd \
 	--with-libmount \
+	--with-modern-grub \
 	--with-soup \
 	--with-selinux \
 	--with-systemdsystemgeneratordir=/lib/systemd/system-generators \