match http:// and https:// assets

this could be also something like that `http[s]?://`

this allows to include http and https resources
```js
sassdown: {
    styleguide: {
        options: {
            assets: [
                "public/styleguide/styles.css",
                "http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js",
                "https://ajax.googleapis.com/ajax/libs/swfobject/2.2/swfobject.js"
            ]
        }
    }
}
```