Add forgotten security fix to 2.3 changelog.

debian/changelog

@@ -4,6 +4,7 @@ tails (2.3) unstable; urgency=medium
     - Upgrade Tor Browser to 5.5.5. (Fixes: #11362)
     - Upgrade icedove to 38.7.0-1~deb8u1
     - Upgrade git to 1:2.1.4-2.1+deb8u2
+    - Upgrade libgd3 to 2.1.0-5+deb8u1
     - Upgrade pidgin-otr to 4.0.1-1+deb8u1
     - Upgrade srtp to 1.4.5~20130609~dfsg-1.1+deb8u1
     - Upgrade imagemagick to 8:6.8.9.9-5+deb8u1