fix shorten IA for new IA API

Shorten IA is currently broken (see https://duckduckgo.com/?q=shorten+https%3A%2F%2Fdylansserver.com), this fixes it.

Also should probably close this: https://duck.co/ideas/idea/1199/shortening-url-service (although I second a ddg.gg service).
@nospampleasemam now that I'm thinking about it a bit more, perhaps we don't need to handle the mobile case specially at all. In either case, I think the `<input>` is the best because after a click it'll get highlighted for copying (I'm assuming anytime someone is shortening a URL they care more about copy/pasting it somewhere rather than going to the URL they just entered).

Thoughts?