Settings: fix CANCELLATION_AT_PERIOD_END
Settings: fix CANCELLATION_AT_PERIOD_END

This setting was being ignored, and instead was depended on the proration policy
because of a back copy and paste.
pydanny/dj-stripe,kavdev/dj-stripe,kavdev/dj-stripe,pydanny/dj-stripe,dj-stripe/dj-stripe,dj-stripe/dj-stripe