css loaded from another domain, skip it

I'm using external fonts on my page

`<link href='http://fonts.googleapis.com/css?family=Open+Sans:400italic,400,300,600' rel='stylesheet' type='text/css' />`

and I was getting on Firefox 

>SecurityError: The operation is insecure.
>var rules = sheets[i].cssRules;

As the script iterates over all the styles of the page, in my case the svg is in a page that contains more data, and the style files could related to the other content, so I found kind of frustrating for it to just crashed on Firefox.


On the other hand, after doing this "patch" on the code I found out that adding the [**crossorigin**](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/link#attr-crossorigin) attribute to the link tag would fixed my problem also.

I'm not sure what is the more general solution, maybe just add a note on the readme file about the [**crossorigin**] attribute is going to be enough.

Thanks for the library :+1: