Update 15_day_classes.md

line 114 should be like this;
Person { firstName: undefined, lastName: undefined }

15_Day_Classes/15_day_classes.md

@@ -111,7 +111,7 @@ console.log(person)
 ```
 
 ```sh
-Person {firstName: undefined, lastName}
+Person { firstName: undefined, lastName: undefined }
 ```
 
 All the keys of the object are undefined. When ever we instantiate we should pass the value of the properties. Let us pass value at this time when we instantiate the class.