fix the fingerprint namespace?

I see that  http://xmpp.org/extensions/xep-0320.html has defined a formal namespace for the dtls fingerprint.

Any chance of adopting it ?

```
   <fingerprint xmlns='urn:xmpp:jingle:apps:dtls:0' hash='sha-256' setup='actpass'>
      02:1A:CC:54:27:AB:EB:9C:53:3F:3E:4B:65:2E:7D:46:3F:54:42:CD:54:F1:7A:03:A2:7D:F9:B0:7F:46:19:B2
    </fingerprint>
```
