Ducktype in _.isError for ES6 support.

lodash.js

@@ -9871,9 +9871,8 @@
       if (!isObjectLike(value)) {
         return false;
       }
-      var Ctor = value.constructor;
       return (objectToString.call(value) == errorTag) ||
-        (typeof Ctor == 'function' && objectToString.call(Ctor.prototype) == errorTag);
+        (typeof value.message == 'string' && typeof value.name == 'string');
     }
 
     /**

test/test.js

@@ -364,7 +364,9 @@
     this.message = message;
   }
 
-  CustomError.prototype = lodashStable.create(Error.prototype);
+  CustomError.prototype = lodashStable.create(Error.prototype, {
+    'constructor': CustomError
+  });
 
   /**
    * Removes all own enumerable properties from a given object.