Consider BIC in Stripe 2.0

[paltman]

Issue Summary

A new version of the python library for Stripe was released and includes some backwards incompatible changes.

We should test and address them:

https://github.com/stripe/stripe-python/blob/master/CHANGELOG.md#200---2018-07-10

[blueyed]

#574
(1 week older than this issue already)

[blueyed]

For now I think stripe-python should be pinned at least.

[paltman]

@blueyed Sorry that I missed your PR. I've been away from Pinax for a bit due to work commitments. Looking to catch back up shortly but these seem priority. My plan is to do the following:

1. Release a new minor version of pinax-stripe (v4.4.0) pinned to stripe-python<2,>=1.7.9
2. Merge Support stripe-python 2.0 #574
3. Release a new minor version (since the change should be BC with integrations, I don't think it warrants a major version bump) of pinax-stripe (v4.5.0) pinned to stripe-python>=2

[paltman]

I suspect the dependency caching in CI has prevented errors from triggering