make changes files pass lintChanges as appropriate

changes/bug17702

@@ -1,4 +1,4 @@
-  o Major bugfixes:
+  o Major bugfixes (voting):
     - Actually enable Ed25519-based directory collation.
       Previously, the code had been written, but some debugging code that had
       accidentally been left in the codebase made it stay turned off.

changes/bug18318_ed

@@ -1,4 +1,4 @@
-  o Major bugfixes:
+  o Major bugfixes (voting):
     - When generating a vote with keypinning disabled, never include two
       entries for the same ed25519 identity.  This bug was causing
       authorities to generate votes that they could not parse when a router

changes/bug18368

@@ -1,4 +1,4 @@
-  o Minor bugfixes:
+  o Minor bugfixes (logging):
     - When logging information about an unparseable networkstatus vote or
       consensus, do not say "vote" when we mean consensus. Fixes bug
       18368; bugfix on 0.2.0.8-alpha.