Update changelog for 1.8.2.

debian/changelog

-tails (1.8.2) UNRELEASED; urgency=medium
+tails (1.8.2) unstable; urgency=medium
 
-  * Dummy entry for next release.
-
- -- Tails developers <tails@boum.org>  Sun, 20 Dec 2015 14:09:33 +0000
+  * Security fixes
+    - Upgrade Tor Browser to 5.0.7.
+    - Upgrade Linux to 3.16.7-ckt20-1+deb8u2.
+    - Upgrade foomatic-filters to 4.0.17-1+deb7u1.
+    - Upgrade git to 1:1.7.10.4-1+wheezy2.
+    - Upgrade Icedove to 38.5.0-1~deb7u1.
+    - Upgrade libxml2-related packages to 2.8.0+dfsg1-7+wheezy5.
+    - Upgrade OpenSSL-related packages to 1.0.1e-2+deb7u19.
+
+ -- Tails developers <tails@boum.org>  Sat, 09 Jan 2016 16:27:27 +0100
 
 tails (1.8.1) unstable; urgency=medium