Stripe is putting out console warnings in tests

# Problem

A bunch of our tests, when executed, output a `console.warn` into the terminal, with

```
You may test your Stripe.js integration over HTTP. However, live Stripe.js integrations must use HTTPS.
```

This pollutes the test output, which

- makes it more difficult to see which test failed when executing `ember-exam`
- makes it more difficult to see why and which tests failed on circle
- implies our tests may be contacting the stripe API, which possibly should not have to happen

We should

- identify where the warning is being called
- figure out if it's due to contacting the stripe API
- figure out how to either avoid, or, if not possible, squelch it