Mark Tails 3.0~rc1 as released.

debian/changelog

-tails (3.0~rc1) UNRELEASED; urgency=medium
+tails (3.0~rc1) unstable; urgency=medium
 
   * Major changes
     - Install Thunderbird 1:45.8.0-3+tails2 and handle the Icedove → Thunderbird
@@ -127,7 +127,7 @@ tails (3.0~rc1) UNRELEASED; urgency=medium
       machine type, for reproducibility testing (refs: #12345).
     - Add support for installing Tor Browser nightly builds.
 
- -- Tails developers <tails@boum.org>  Sat, 20 May 2017 13:45:29 +0200
+ -- Tails developers <tails@boum.org>  Sat, 20 May 2017 16:48:45 +0200
 
 tails (3.0~beta4) unstable; urgency=medium