mention the bug number in the 6827 changes file

changes/bug6827

@@ -4,5 +4,6 @@
       rendezvous/introduction protocols in a hidden service
       descriptor.  Previously, Tor would have confused (as-yet-unused)
       protocol version numbers greater than 32 with lower ones on many
-      platforms.  Bugfix on 0.2.0.10-alpha; found by George Kadianakis.
+      platforms.  Fixes bug 6827; bugfix on 0.2.0.10-alpha; found by
+      George Kadianakis.