Update Utility.php

[lbuguellou]

Create Stripe InvoiceItem accept price identifier in "price" attributes but with the converter on price and amount, this identifier is transformed to integer and not correspond to a StripePriceId

I propose to use a boolean attribute "conversion" to bypass this conversion if needed like :

Stripe::invoiceItems()->create('cus_ndfjshjfdhf45456', [ 'price' => 'price_hjhghdqezei1545', 'conversion' => false, ]);

[brunogaspar]

Not really a fan of passing such parameters around, seems that just checking if the value of amount is numeric would be a tad better i think.

In any case, it would need tests.