Update changelog

Author: Crozzers

CHANGES.md

@@ -6,6 +6,7 @@
 - [pull #622] Add missing block tags to regex (#620)
 - [pull #623] Don't escape plus signs in URLs (#621)
 - [pull #626] Fix XSS when encoding incomplete tags (#625)
+- [pull #628] Fix TypeError in MiddleWordEm extra when options was None (#627)
 
 
 ## python-markdown2 2.5.3