Error in testing when updating arguments passed to stripe components

Even though we have turned the `mock` config option on during testing, we still get an error about a missing method, `update`, when running our test suite:

> Uncaught TypeError: `Ember.get(...).update` is not a function

It's pointing to here:

https://github.com/code-corps/ember-stripe-elements/blob/74540fc5ed106b86916eef2c29059e231095903d/addon/components/stripe-element.js#L54-L57

I'm guessing this is just because that method isn't mocked in your `StripeMock` class and that's merely because you don't have any tests that try to update the attributes after rendering. Replacing your mock with our own copy which also mocks the `update` function makes our tests pass again.

Start with addon/components/stripe-element.js at lines 54-57, then inspect the StripeMock class and run the test suite to reproduce the missing update method. Add coverage for updating component arguments after rendering, and consider the issue done when the mock supports that call and the tests pass without the TypeError.

Written by the indexing model from the issue text.