The pep257 dependency does not support Python 3.10 and has been
deprecated in favour of flake8-docstrings. While we're here, we bump the
other linter dependencies and remove a note regarding the order of
dependencies, which is no longer true with the new dependency resolver
introduced in pip 20.3. We also remove an import exception for six.moves
since we no longer use six.
Change-Id: I4aae75f513568126230becf27b2e07d6682d35a1
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>
6dfde5b48b