Mark Tails 3.4 as released.

debian/changelog

-tails (3.4) UNRELEASED; urgency=medium
+tails (3.4) unstable; urgency=medium
 
   * Security fixes
     - Install Linux 4.14.0-2 from sid (Closes: #14976). This enables
@@ -105,7 +105,7 @@ tails (3.4) UNRELEASED; urgency=medium
     - Hot-plug a 'pcnet' network device instead of 'virtio' on Sid,
       since the latter is not detected on Sid (Closes: #14819).
 
- -- Tails developers <tails@boum.org>  Mon, 08 Jan 2018 14:14:05 +0100
+ -- Tails developers <tails@boum.org>  Mon, 08 Jan 2018 16:57:07 +0100
 
 tails (3.3) unstable; urgency=medium