Wrong Web IDL type for URLs in Digital Goods API

[dontcallmedom-bot]

While crawling Digital Goods API, wrong Web IDL type for URLs:

• field iconURLs in dictionary ItemDetails uses DOMString instead of recommended USVString for URLs

_{Cc @dontcallmedom @tidoust}

_{This issue was detected and reported semi-automatically by Strudy based on data collected in webref.}