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).
Problem with this is that it fails if we just type in `shorten duckduckgo.com` since the regexp _requires_ that `https?` exists in the string.

In this code,
```perl
my @matches = m|(https?)(?:://)?(.+)| =~ shift;
```
matches is empty for `shorten duckduckgo.com` (please add this to the test too)