Support URIBLs

[theel0ja]

Fixes #10

Code I used for dev purposes: https://gist.github.com/theel0ja/28f9b2c6fbe3d6d5fc4547680b211fcc

includeTxt is broken, though.

I guess it's this:

dnsbl/index.js

Lines 35 to 37 in 5c340a5

	} catch (err) {
	return opts.includeTxt ? {listed: false, txt: []} : false;
	}

It returns "false" even if the A record is returned, if no TXT record exists on the URIBL