Fix typo.

debian/changelog

 tails (1.0~rc1) unstable; urgency=medium
 
   * Bugfixes
-    - Disble inbound I2P connections. Tails already restricts incoming
+    - Disable inbound I2P connections. Tails already restricts incoming
       connections, but this change tells I2P about it.
     - Fix link to the system requirements documentation page in the Tails
       Upgrader error shown when too little RAM is available.