chore(deps): update dependency gunicorn to v20.1.0

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
gunicorn (source)	==20.0.4 -> ==20.1.0

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Release Notes

benoitc/gunicorn (gunicorn)

v20.1.0

Compare Source

• document WEB_CONCURRENCY is set by, at least, Heroku
• capture peername from accept: Avoid calls to getpeername by capturing the peer name returned by
  accept
• log a warning when a worker was terminated due to a signal
• fix tornado usage with latest versions of Django
• add support for python -m gunicorn
• fix systemd socket activation example
• allows to set wsgi application in configg file using wsgi_app
• document --timeout = 0
• always close a connection when the number of requests exceeds the max requests
• Disable keepalive during graceful shutdown
• kill tasks in the gthread workers during upgrade
• fix latency in gevent worker when accepting new requests
• fix file watcher: handle errors when new worker reboot and ensure the list of files is kept
• document the default name and path of the configuration file
• document how variable impact configuration
• document the $PORT environment variable
• added milliseconds option to request_time in access_log
• added PIP requirements to be used for example
• remove version from the Server header
• fix sendfile: use socket.sendfile instead of os.sendfile
• reloader: use absolute path to prevent empty to prevent0 InotifyError when a file
  is added to the working directory
• Add --print-config option to print the resolved settings at startup.
• remove the --log-dict-config CLI flag because it never had a working format
  (the logconfig_dict setting in configuration files continues to work)

** Breaking changes **

• minimum version is Python 3.5
• remove version from the Server header

** Documentation **

** Others **

• miscellaneous changes in the code base to be a better citizen with Python 3
• remove dead code
• fix documentation generation

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