Modify extend_match for use in Python

Signed-off-by: Jono Yang <jyang@nexb.com>

Author: JonoYang

src/licensedcode/_seq.py.ABOUT

@@ -17,7 +17,7 @@ owner: nexB
 
 license_expression: python
 licenses:
--   file: seq.py.LICENSE
+-   file: _seq.py.LICENSE
     key: python
     name: Python Software Foundation License v2