flake8 new release 3.8.0 added new checks and gate pep8
job start failing. hacking 3.0.1 fix the pinning of flake8 to
avoid bringing in a new version with new checks.
Though it is fixed in latest hacking but 2.0 and 3.0 has cap for
flake8 as <4.0.0 which mean flake8 new version 3.9.0 can also
break the pep8 job if new check are added.
To avoid similar gate break in future, we need to bump the hacking min
version.
- http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014828.html
Change-Id: I84b77958d7dfeedca44e8718554ede24b006746f
(cherry picked from commit ee4dc0173b)
Mistral Extra is a library which allows contributors to add optional
functionality to the mistral project, it also contains examples for
which to base new capabilities.