changelog: fixup Linux version for Tails 2.12.

debian/changelog

@@ -4,7 +4,7 @@ tails (2.12) unstable; urgency=medium
     - Completely remove I2P. :( We have decided to remove I2P (see
       #11276) due to our failure of finding someone interested in
       maintaining it in Tails (Closes: #12263).
-    - Upgrade the Linux kernel to 4.9.0-0.bpo.2 (Closes: #12122).
+    - Upgrade the Linux kernel to 4.9.13-1~bpo8+1 (Closes: #12122).
 
   * Security fixes
     - Upgrade Tor Browser to 6.5.2 based on Firefox 45.9. (Closes: