Changelog: fix typos.

debian/changelog

@@ -8,12 +8,12 @@ tails (3.6~rc1) unstable; urgency=medium
 
   * Major changes
     - Upgrade Tor to 0.3.2.9. (Closes: #15158)
-    - Add ability to lock the screen (Closes: #5684)
+    - Add ability to lock the screen. (Closes: #5684)
     - Add support for meek_lite bridges. (Closes: #8243)
     - Upgrade to Thunderbird 52.6.0. (Closes: #15298)
     - Enable Thunderbird AppArmor profile. (Closes: 11973)
     - Upgrade Linux to 4.15.0-1. (Closes: #15309).
-    - Upgrade Systemd to v237.
+    - Upgrade systemd to 237.
     - Upgrade Electrum to 3.0.6. (Closes: #15022)
     - Port most of Tails shell scripts to Python thanks to
       GoodCrypto. (Closes: #11198)