Merge pull request #31 from xiaofen9/master

fix type checking vul in ctorName

index.js

@@ -66,7 +66,7 @@ module.exports = function kindOf(val) {
 };
 
 function ctorName(val) {
-  return val.constructor ? val.constructor.name : null;
+  return val.constructor && typeof val.constructor === 'function' ? val.constructor.name : null;
 }
 
 function isArray(val) {