Update WhazzupGreeting link (#592)

README.md

@@ -10,7 +10,7 @@ Plugin Framework for Java (PF4J)
 A plugin is a way for a third party to extend the functionality of an application. A plugin implements extension points
 declared by application or other plugins. Also, a plugin can define extension points.  
 
-**NOTE:** Starting with version 0.9 you can define an extension directly in the application jar (you're not obligated to put the extension in a plugin - you can see this extension as a default/system extension). See [WhazzupGreeting](https://github.com/pf4j/pf4j/blob/master/demo/app/src/main/java/org/pf4j/demo/WhazzupGreeting.java) for a real example.  
+**NOTE:** Starting with version 0.9 you can define an extension directly in the application jar (you're not obligated to put the extension in a plugin - you can see this extension as a default/system extension). See [WhazzupGreeting](https://github.com/pf4j/pf4j/blob/master/demo/gradle/app/src/main/java/org/pf4j/demo/WhazzupGreeting.java) for a real example.  
 
 Features/Benefits
 -------------------