Updating Examples/get-rates-to-show-customer.php based on API Changes

[jippylong12]

These examples have not been updated in many moons and the API has changed. I'm sure all the others will need to be redone in some capacity, but I was just fixing this since I used it

Shippo_Shipment no longer accepts the 'parcels' key and instead only 'parcel' The $shipment key is now 'rates_list' instead of 'rates'