Explain cryptic JSHint incantation (close #18)

^_^
yes! I added a comment related to this a while ago: https://github.com/mozilla/node-firefox-ports/pull/10#discussion_r21742011 it doesn't scroll well because it's "an outdated commit" but this could be an alternative:

```javascript
if(matches) {
  var port = Number(matches[3]);
  var pid = Number(matches[2]);
  if(port !== MARIONETTE_PORT) {
    ports.push({ type: matches[1], port: port, pid: pid });
  }
}
```