Mark Tails 3.6.1 as released.

debian/changelog

-tails (3.6.1) UNRELEASED; urgency=medium
+tails (3.6.1) unstable; urgency=medium
 
   * Security fixes
     - Upgrade Tor Browser to 7.5.2 (MFSA 2018-08 i.e. CVE-2018-5146).
@@ -12,7 +12,7 @@ tails (3.6.1) UNRELEASED; urgency=medium
       in non-release builds
       (https://trac.torproject.org/projects/tor/ticket/24912#comment:8).
 
- -- Tails developers <tails@boum.org>  Fri, 16 Mar 2018 21:07:36 +0000
+ -- Tails developers <tails@boum.org>  Fri, 16 Mar 2018 22:42:00 +0000
 
 tails (3.6) unstable; urgency=medium