Update FlexiFormatter release to v3.10

Author: davesteele

Doc/library/argparse.rst

@@ -490,7 +490,7 @@ single non-whitespace character followed by a "."::
      -h, --help  show this help message and exit
 
 
-.. versionchanged:: 3.9
+.. versionadded:: 3.10
    :class:`FlexiHelpFormatter` class was added.
 
 :class:`ArgumentDefaultsHelpFormatter` automatically adds information about