config: use mini-os master for unstable

We haven't used mini-os master for about 2 years now due to a stubdom
test failing [1]. Booting a guest with mini-os master used for building
stubdom didn't reveal any problem, so use master for unstable in order
to let OSStest find any problems not showing up in the local test.

[1]: https://lists.xen.org/archives/html/minios-devel/2018-04/msg00015.html

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>

Config.mk

@@ -245,7 +245,7 @@ MINIOS_UPSTREAM_URL ?= git://xenbits.xen.org/mini-os.git
 endif
 OVMF_UPSTREAM_REVISION ?= 20d2e5a125e34fc8501026613a71549b2a1a3e54
 QEMU_UPSTREAM_REVISION ?= master
-MINIOS_UPSTREAM_REVISION ?= 0b4b7897e08b967a09bed2028a79fabff82342dd
+MINIOS_UPSTREAM_REVISION ?= master
 
 SEABIOS_UPSTREAM_REVISION ?= rel-1.13.0