Set CheckoutUtility URL

[timtait]

The client.rb class was missing a case to set the base service URL of the CheckoutUtility.

To test, from the root directory -

irb
require_relative "lib/adyen"
client = Adyen::Client.new(env: :test, api_key: "XXX")
client.checkout_utility.origin_keys(originDomains: ["http://127.0.0.1"])

master
=> ArgumentError: Invalid service specified

checkout-utility-url
=> "{\"originKeys\":{\"http:\\/\\/127.0.0.1\":\"pub.v2.XXX\"}}"

[crrood]

Hi Tim,

Thanks for the pull request! Merging into develop branch.