/**
* Minify css string.
* @function lib.minify.minifyCssString
* @param {string} src - Source css string.
* @param {function} callback - Callback when done.
* @author Taka Okunishi
*
*/
module.exports = function (src, callback) {
var CleanCSS = require('clean-css');
var minimized = new CleanCSS().minify(src);
callback(null, minimized);
};