SVG_PATTERN fix for multiline rules

Multiline rules like this are not matched by svg preprocessor:
background-image: url('./img/icon.svg') svg({
    path#p1 { fill: #00FF00; }
    path[id="p2"] { fill: #FF0000; }
});

The cause is you are not matching new lines characters. I have fixed it by swapping dot for [\s\S].
I have also added a few tests for this pattern while debugging and updated lib to be more testable.