CDN with multiple background images.

Hey,

Awesome plugin. It “just worked” except for one little thing. I have multiple background images defined in CSS like this:

background-image: url("images/under-left-leaf.png"), url("images/over-blue-bird.png"), url("images/under-top.png"), url("images/bg-top-grunge.png");

After this goes through autoptimize it only applies the CDN to the first image, like this ( theme-cdn.dtbaker.net is the CDN address, verge-blog-demo.themes.dtbaker.net is the hostname )

background-image:url(https://theme-cdn.dtbaker.net/wp-content/themes/verge-blog/images/under-left-leaf.png),url(//verge-blog-demo.themes.dtbaker.net/wp-content/themes/verge-blog/images/over-blue-bird.png),url(//verge-blog-demo.themes.dtbaker.net/wp-content/themes/verge-blog/images/under-top.png),url(//verge-blog-demo.themes.dtbaker.net/wp-content/themes/verge-blog/images/bg-top-grunge.png);

Do you accept pull requests via github? I could submit a patch if you like.

Thanks,
dtbaker