Make the CSS "url()" regex less strict on cachebusters

Some libraries like FontAwesome come with their own cache buster [1] that
looks like this "file?v=123#hash". This kind of url wasn't recognized and
expended by Jammit due to a restrictive regex.

[1] https://github.com/FortAwesome/Font-Awesome/blob/5a7e14b7cf5252702c4cf5da043cd73852e6f17a/css/font-awesome.css#L9-L10