Mark Tails 4.0~rc1 as released.

debian/changelog

-tails (4.0~rc1) UNRELEASED; urgency=medium
+tails (4.0~rc1) unstable; urgency=medium
 
   * Major changes
     - Update Tor Browser to 9.0a7, based on Firefox ESR 68 (#16356).
@@ -132,7 +132,7 @@ tails (4.0~rc1) UNRELEASED; urgency=medium
     - Fix regression in the Persistent browser bookmarks scenario
       (Closes: #17125).
 
- -- Tails developers <tails@boum.org>  Thu, 10 Oct 2019 07:57:23 +0000
+ -- Tails developers <tails@boum.org>  Thu, 10 Oct 2019 11:23:53 +0000
 
 tails (4.0~beta2) unstable; urgency=medium