[AIRFLOW-2767] Upgrade gunicorn to 19.5.0 to avoid moderate-severit…

[RosterIn]

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-2767
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.

Description

• Here are some details about my PR, including screenshots of any UI changes:

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.
  • All the public functions and the classes in the PR contain docstrings that explain what it does

Code Quality

• Passes flake8

[Fokko]

I've restarted the Kubernetes tests

[Fokko]

Oops, did not mean to close the pr.

[codecov-io]

Codecov Report

Merging #4795 into master will increase coverage by 0.77%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4795      +/-   ##
==========================================
+ Coverage   74.44%   75.22%   +0.77%     
==========================================
  Files         450      450              
  Lines       28970    30099    +1129     
==========================================
+ Hits        21567    22641    +1074     
- Misses       7403     7458      +55

Impacted Files	Coverage Δ
airflow/task/task_runner/base_task_runner.py	78.57% <0%> (-0.74%)	⬇️
...irflow/contrib/example_dags/example_gcp_spanner.py	0% <0%> (ø)	⬆️
.../kubernetes_request_factory/pod_request_factory.py	100% <0%> (ø)	⬆️
airflow/ti_deps/dep_context.py	100% <0%> (ø)	⬆️
airflow/models/taskreschedule.py	100% <0%> (ø)	⬆️
airflow/operators/python_operator.py	96.63% <0%> (+0.8%)	⬆️
airflow/models/__init__.py	94.05% <0%> (+1.4%)	⬆️
airflow/contrib/utils/gcp_field_validator.py	93.67% <0%> (+2.14%)	⬆️
airflow/utils/dates.py	85.71% <0%> (+2.2%)	⬆️
airflow/contrib/hooks/gcp_vision_hook.py	86.36% <0%> (+3.5%)	⬆️
... and 1 more

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[feng-tao]

thanks @RosterIn