fix name typo

CHANGED.txt → CHANGES.txt

+CHANGES
+=======
 
 4.0.0a1 (2012-11-19)
-====================
+--------------------
 
 First (in a long time) separate ZEO release.
 
 Since ZODB 3.10.5:
 
-New Features
-------------
-
 - Storage servers now emit Serving and Closed events so subscribers
   can discover addresses when dynamic port assignment (bind to port 0)
   is used. This could, for example, be used to update address