Update changelog for 3.8.

debian/changelog

 tails (3.8) UNRELEASED; urgency=medium
 
-  * Dummy entry for next release.
+  * Security fixes
+    - Upgrade Tor Browser to 7.5.6 (Closes: #15683).
+    - Upgrade Enigmail to 2.0.7 (partly fixes #15602 aka. EFAIL).
+    - Upgrade libgcrypt to 1.7.6-2+deb9u3 (DSA-4231-1).
+    - Upgrade perl to 5.24.1-3+deb9u4 (DSA-4226-1).
+
+  * Bugfixes
+    - Thunderbird: fix importing public OpenPGP keys from email attachments
+      (Closes: #15610).
+    - Make the Unsafe Browser home page translatable again (Closes: #15461).
+
+  * Minor improvements
+    - Don't display the "Know your rights" message on Thunderbird first run.
+    - Move Thunderbird's default userChrome.css to /etc/thunderbird, just like
+      we do for Tor Browser, for easier upgrade handling.
 
- -- Tails developers <tails@boum.org>  Sun, 10 Jun 2018 16:12:57 +0000
+ -- Tails developers <tails@boum.org>  Mon, 25 Jun 2018 08:02:09 +0000
 
 tails (3.7.1) unstable; urgency=medium