Mark Tails 2.6 as released.

debian/changelog

-tails (2.6) UNRELEASED; urgency=medium
+tails (2.6) unstable; urgency=medium
 
   * Major new features and changes
     - Install Tor 0.2.8.7. (Closes: #11351)
@@ -97,7 +97,7 @@ tails (2.6) UNRELEASED; urgency=medium
       take this into account when budgeting RAM to the isotesters on
       Jenkins.
 
- -- Tails developers <tails@boum.org>  Tue, 07 Jun 2016 09:07:40 +0200
+ -- Tails developers <tails@boum.org>  Tue, 20 Sep 2016 04:16:33 +0200
 
 tails (2.5) unstable; urgency=medium