[Bug] The stylesheet rules is wrong when css includes :not()

[lwenn]

Run this code:

var mensch = require('mensch');
var parsed = mensch.parse('.my-class:not(.class1, .class2) {}', {
  position: true,
  comments: true,
});

The parsed.stylesheet.rules will be an array with two items: ['.my-class:not(.class1', '.class)'], this rules are wrong.
It should not be splited by , simply.