Updates for March 31

[Brandur]

Hi everyone,

Please see below for the Stripe API and bindings changes since last week!

== API
- We have added the ability to preview the application of a coupon in a customer's upcoming invoice. Official documentation here: https://stripe.com/docs/api#upcoming_invoice-coupon

== API Libraries
- stripe-php version 3.12.0 has been released. Changelog: https://github.com/stripe/stripe-php/blob/master/CHANGELOG.md
- stripe-python version 1.32.0 has been released. Changelog: https://github.com/stripe/stripe-python/blob/master/CHANGELOG
- stripe-ruby version 1.39.0 has been released. Changelog: https://github.com/stripe/stripe-ruby/blob/master/History.txt

Brandur