Bump gunicorn from 19.6.0 to 20.1.0

[dependabot]

Bumps gunicorn from 19.6.0 to 20.1.0.

Release notes

Sourced from gunicorn's releases.

20.1.0

• 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

20.0.4

• fix binding a socket using the file descriptor
• remove support for the bdist_rpm build

20.0.3

• fixed load of a config file without a Python extension

... (truncated)

Commits

• 61ccfd6 bump to 20.1.0
• d1f0f11 fix inline code syntax in news
• f87882e add an empty line in news.rst
• 7a79808 update changeslog
• 6fd97b9 Document that WEB_CONCURRENCY is set by, at least, Heroku
• dad99a1 Update gunicorn_ext.py
• 3273492 Improve settings documentation
• 86eac4c Merge pull request #2479 from benoitc/capture-peer-name
• 03c642e Merge pull request #2480 from kofrezo/update_docs_install
• a4407ab Default to Python 3 version of gunicorn in Stretch
• Additional commits viewable in compare view

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[rtibbles]

These are the only breaking changes from the log, so this might be fine?

minimum version is Python 3.5
remove version from the Server header