Update changelog for strong-emphasis fix

Update the changelog in relation to the fix applied in
078f76a (PR #545).

Author: fghaas

CHANGES.md

@@ -4,7 +4,7 @@
 
 - [pull #547] Update `markdown-in-html` extra to handle markdown on same line as HTML (#546)
 - [pull #550] Fix tables with trailing whitespace not being recognized (#549)
-
+- [pull #545] Fix multiple instances of strong emphasis (`**`) in one line (#541)
 
 ## python-markdown2 2.4.11