Fix bug: facebox content was not properly centered

In jQuery 1.8.3, the outerWidth() API returns a jQuery Object, not a number, so we should use the following code:

```javascript

$('#facebox').show().css({
  ...
  left:  $(window).width() / 2 - ($('#facebox .popup').outerWidth(true) / 2)
})
```

By the way, this commit also upgrades facebox.js to the latest version.