Updates an existing cart as per provided model.

curl --request PUT \
     --url /api/episerver/v3.0/me/carts \
     --header 'accept: application/json' \
     --header 'content-type: application/json' \
     --data '{
     "name": "",
     "market": "",
     "currency": "",
     "shipments": [
     {
     "lineItems": [
     {
     "quantity": ""
     }
     ]
     }
     ]
     }'