Fixed bug to not add root url for protocl relative urls.

Example I use http://www.paulirish.com/2010/the-protocol-relative-url/ in html layout.

```html
<link href='//fonts.googleapis.com/css?family=Open+Sans:400,600' rel='stylesheet' type='text/css'>
```
and after run `translate_path` I got next:

```html
<link href='http://example.com/fonts.googleapis.com/css?family=Open+Sans:400,600' rel='stylesheet' type='text/css'>
```