update flake8 config
update flake8 config

flake8 3 has broken defaults, so we have to whitelist instead of just blacklist
yuvipanda/mwoauthenticator,enolfc/oauthenticator,santi81/oauthenticator,minrk/oauthenticator,NickolausDS/oauthenticator,yuvipanda/mwoauthenticator,luisfdez/oauthenticator,luisfdez/oauthenticator,jupyterhub/oauthenticator,jupyter/oauthenticator,maltevogl/oauthenticator,santi81/oauthenticator,jupyter/oauthenticator