FIX: use stylus nodes api to properly inject url literal

The stylus extension function used within both express example projects is not working.

The background image style is rendering incorrectly as a quoted string.

```css
#break
{
  background-image: 'url("/images/v0.1/background.png")';
}
```

Stylus provides  a Literal object from the nodes API that can correct this and make it look as follows.

```css
#break {
  background-image: url("/images/background.png");
}
```