fixed closing bracket for url not showing

lib/less/node/url.js

@@ -5,6 +5,6 @@ tree.URL = function URL(val) {
 };
 tree.URL.prototype = {
     toCSS: function () {
-        return "url(" + (this.value.toCSS ? this.value.toCSS() : this.value + ")");
+        return "url(" + (this.value.toCSS ? this.value.toCSS() : this.value) + ")";
     }
 };