Fix isort v5 deprecated config

[jamescooke]

=== isort ===                                                                                            
isort --quiet --recursive --diff setup.py src/flake8_aaa tests > isort.out                               
/home/james/active/flake8-aaa/.tox/py36-lint/lib/python3.6/site-packages/isort/main.py:718: UserWarning: 
                                                                                                         
The following deprecated CLI flags were used: --recursive!                                               
Please see the 5.0.0 upgrade guide:                                                                      
        https://timothycrosley.github.io/isort/docs/upgrade_guides/5.0.0/                                
                                                                                                         
  f"\n\nThe following deprecated CLI flags were used: {', '.join(deprecated_flags)}!\n"                  
/home/james/active/flake8-aaa/.tox/py36-lint/lib/python3.6/site-packages/isort/settings.py:329: UserWarning: 

The following deprecated settings was used: not_skip!
Please see the 5.0.0 upgrade guide:
        https://timothycrosley.github.io/isort/docs/upgrade_guides/5.0.0/

  f"\n\nThe following deprecated settings was used: {deprecated_option}!\n"
if [ "$(wc -l isort.out)" != "0 isort.out" ]; then cat isort.out; exit 1; fi

Also using wc might be avoidable now.