Mark Tails 3.9.1 as released.

debian/changelog

-tails (3.9.1) UNRELEASED; urgency=medium
+tails (3.9.1) unstable; urgency=medium
 
   * Security fixes
     - Upgrade Tor Browser to 8.0.2, based on Firefox 60.2.1 (Closes: #16017).
@@ -28,7 +28,7 @@ tails (3.9.1) UNRELEASED; urgency=medium
   * Minor improvements and updates
     - Upgrade tor to 0.3.4.8-1~d90.stretch+1 (Closes: #15889).
 
- -- Tails developers <tails@boum.org>  Mon, 01 Oct 2018 14:00:26 +0000
+ -- Tails developers <tails@boum.org>  Wed, 03 Oct 2018 12:12:33 +0200
 
 tails (3.9) unstable; urgency=medium