Update sysutils/py-supervisor to 4.2.1
Changelog for 4.2.1:
- Fixed a bug on Python 3 where a network error could cause supervisord to crash with the error <class 'TypeError'>:can't concat str to bytes.
- Fixed a bug where a test would fail on systems with glibc 2.3.1 because the default value of SOMAXCONN changed.
And while I'm here, also clean some style nits.