brew upgrade ruby-install
ruby-install ruby 2.6.5
Depending on ruby version manager (rvm/chruby/rbenv) you may need to change directories or select ruby 2.6.5 then
config.authentication_method = :authenticate_admin_user! | |
config.current_user_method = :current_admin_user | |
config.logout_link_path = :destroy_user_session_path |