Bump gunicorn from 19.4.5 to 19.5.0 in /imagesite/install

[dependabot]

Bumps gunicorn from 19.4.5 to 19.5.0.

Release notes

Sourced from gunicorn's releases.

19.5.0

== 19.5.0 ==

=== Core ===

• fix: Ensure response to HEAD request won't have message body
• fix: lock domain socket and remove on last arbiter exit (#1220)
• improvement: use EnvironmentError instead of socket.error (#939)
• add: new $FORWARDDED_ALLOW_IPS environment variable (#1205)
• fix: infinite recursion when destroying sockets (#1219)
• fix: close sockets on shutdown (#922)
• fix: clean up sys.exc_info calls to drop circular refs (#1228)
• fix: do post_worker_init after load_wsgi (#1248)

=== Workers ===

• fix access logging in gaiohttp worker (#1193)
• eventlet: handle QUIT in a new coroutine (#1217)
• gevent: remove obsolete exception clauses in run (#1218)
• tornado: fix extra "Server" response header (#1246)
• fix: unblock the wait loop under python 3.5 in sync worker (#1256)

=== Logging ===

• fix: log message for listener reloading (#1181)
• Let logging module handle traceback printing (#1201)
• improvement: Allow configuring logger_class with statsd_host (#1188)
• fix: traceback formatting (#1235)
• fix: print error logs on stderr and access logs on stdout (#1184)

=== Documentation ===

• Simplify installation instructions in gunicorn.org (#1072)
• Fix URL and default worker type in example_config (#1209)
• update django doc url to 1.8 lts (#1213)
• fix: miscellaneous wording corrections (#1216)
• Add PSF License Agreement of selectors.py to NOTICE (:issue: #1226)
• document LOGGING overriding (#1051)
• put a note that error logs are only errors from Gunicorn (#1124)
• add a note about the requirements of the threads workers under python 2.x (#1200)
• add access_log_format to config example (#1251)

=== Tests ===

• Use more pytest.raises() in test_http.py

Commits

• 7d61a60 add changelog
• 58f190d Merge pull request #1257 from benoitc/fix/1256
• b0c0333 unblock the wait loop under python 3.5
• 9d158be Add access_log_format to config example (#1251)
• ded610e add a note about the requirements of the threads workers under python 2.x
• 6f9ae5e put a note that error logs are only errors from Gunicorn.
• 65db610 print error logs on stderr and access logs on stdout
• 5fa32a6 document LOGGING overriding
• e005c9d reverse change in example_config.py
• 66546d6 fix #1246
• Additional commits viewable in compare view

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