util: removed duplicated isArray check

lib/util.js

@@ -430,8 +430,7 @@ function reduceToSingleString(output, base, braces) {
 // NOTE: These type checking functions intentionally don't use `instanceof`
 // because it is fragile and can be easily faked with `Object.create()`.
 function isArray(ar) {
-  return Array.isArray(ar) ||
-         (typeof ar === 'object' && objectToString(ar) === '[object Array]');
+  return Array.isArray(ar);
 }
 exports.isArray = isArray;