Update README.rst

Author: benkiel

README.rst

@@ -47,4 +47,4 @@ However, the import name for the package remains ``extractor``, without prefix.
    :target: https://github.com/robotools/extractor/actions?query=workflow%3ATests
 .. |PyPI Version| image:: https://img.shields.io/pypi/v/ufo-extractor.svg
    :target: https://pypi.org/project/ufo-extractor/
-.. |Python Versions| image:: https://img.shields.io/badge/python-3.6%2C%203.8-blue.svg
+.. |Python Versions| image:: https://img.shields.io/badge/python-3.7%2C%203.8%2C%203.9-blue.svg