mincss fails to fetch CSS resources referenced via data:text/css @import

E.g., on http://sherwoodcourt.com/, the TripAdvisor CSS is included via:

```
<link href="data:text/css,@import%20url%28%27%20http%3A//static.tacdn.com/css2/widget/cdswidEXC-v22775008216b.css%20%27%29%3B" rel="stylesheet">
```
