Bump gunicorn from 20.0.4 to 21.0.1 in /codalab/requirements

[dependabot]

Bumps gunicorn from 20.0.4 to 21.0.1.

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

Commits

• 547f856 bump 21.0.1: fix doc
• 033dca6 fix doc path to conf.py in readthedocs.yaml
• 1dd24e6 fix .readthedocs.yaml path
• b6eb01b add readthedocs.yaml
• 543628e remove pypy-3.7 from tests
• 91cb3dc Revert "remove cryptography from requirements"
• 471a6f8 remove cryptography from requirements
• f628dd9 fix import error
• cac38b4 bump doc version
• 0304f00 add minitimal changelog
• Additional commits viewable in compare view

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[dependabot]

Superseded by #3405.