- Replace `Charge::refund()` to `Refund::create()`
- Replace `Customer::invoices()` to `Invoice::all()`
- Replace renamed exception classes

After upgrading to the v7 of the Stripe SDK, the `$customer->invoice_settings->default_payment_method` is null.

In that case, we don't need to update the Stripe customer, so we will just update the database.

The previous functionality has been kept as is.

According to laravel#562, the invoice response contains only 10 line items, so we were manually fetching 1000 items.

But Stripe's pagination limit is 100 items, so that doesn't ensure that all the line items will be fetched.

Instead, we can use the `Stripe\Collection::autoPagingIterator()` which automatically fetches all the paginated results with a generator.

I was tempted to use a lazy collection here, but since this method will be called by the `Invoice::invoiceItems()` and `Invoice::subscriptions()` methods, we don't want to hit the API twice just to filter the results.