Switch to using `head` to avoid bogus p tags

I keep getting issues where this attempts to submit a URL with a `</p>` tag to Instapaper.

I found that the output of the "find URLs" item, when pointed at a rich text-derived link like `<a href="http://foo"><p>http://foo</p></a>` often catches the paragraph tags.

Switching to the first URL returned (using `head`) fixes this issue, and will likely make this more reliable when URL-like things appear in link text.