Typo fixed.

Author: Bernhard Reiter

CHANGES.txt

@@ -8,7 +8,7 @@ Entries without name were done by Richard Jones.
 Fixed:
 
 - Do not depend on a CPython implementation detail anymore to make Roundup 
-  more compatible with other Python implementation like PyPy.
+  more compatible with other Python implementations like PyPy.
   Closes issue2550707. Thanks to Christof Meerwald. (Bernhard Reiter)
 - Yet another fix to the mail gateway, messages got *all* files of
   an issue, not just the new ones. Thanks to Rafal Bisingier for