debian/changelog: set prev releases to unstable

Otherwise it fools osmo-release.mk

Change-Id: I6c05bb7f5bb2b3e78283a5eae6ccf95ce86838f8
diff --git a/debian/changelog b/debian/changelog
index e8fb68e..0c11efb 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,10 +1,10 @@
-osmo-iuh (0.2.0) UNRELEASED; urgency=low
+osmo-iuh (0.2.0) unstable; urgency=low
 
   * Upstream 0.2.0 release
 
  -- Harald Welte <laforge@gnumonks.org>  Fri, 27 Oct 2017 22:19:00 +0000
 
-osmo-iuh (0.1.0) UNRELEASED; urgency=low
+osmo-iuh (0.1.0) unstable; urgency=low
 
   * Initial release.