Mark Tails 3.0~beta3 as released.

debian/changelog

-tails (3.0~beta3) UNRELEASED; urgency=medium
+tails (3.0~beta3) unstable; urgency=medium
 
   * Major new features and changes
     - Make the "Formats" settings in Tails Greeter take effect (Closes: #12079,
@@ -72,7 +72,7 @@ tails (3.0~beta3) UNRELEASED; urgency=medium
     - Adjust apt-mirror to support branches based on feature/stretch
       that don't use frozen APT snapshots.
 
- -- Tails developers <tails@boum.org>  Sun, 19 Mar 2017 11:25:28 +0000
+ -- Tails developers <tails@boum.org>  Sun, 19 Mar 2017 15:10:28 +0100
 
 tails (3.0~beta2) unstable; urgency=medium