Update README.md

Author: SrdjanPaunovic

extension-objects/README.md

@@ -13,7 +13,7 @@ tags:
 Anticipate that an object’s interface needs to be extended in the future. Additional
 interfaces are defined by extension objects.
 
-![alt text](./etc/extension_obj1.png "Extension objects")
+![Extension_objects](./etc/extension_obj.png "Extension objects")
 
 ## Applicability
 Use the Extension Objects pattern when: