fix regexp for '@import url()'

Author: s0ph1e

lib/load.js

@@ -241,9 +241,8 @@ var Loader = function (data) {
     var cssLocalDirname = cssLocalPath ? path.dirname(cssLocalPath) : options.path,
       commentRegexp = /\/\*([\s\S]*?)\*\//g,
       sourcesRegexps = [
-        /(url[\s]*\([\s'"]*)(.+?)([\s'"]*\))/gi,
         /(@import[\s]*['"]?[\s]*)(.+?)([\s]*['"]?;)/gi,
-        /(@import[\s]*url[\s]*\([\s'"]*)(.+?)([\s'"]*\))/gi
+        /((?:@import[\s]*)?url[\s]*\([\s'"]*)(.+?)([\s'"]*\))/gi
       ],
       urlPromises = [];