HelloWorld: Modernize

modernize-use-*

Change-Id: I8b53d86b48f3b5c15e6967dd450b814a90987ac1
Reviewed-by: André Hartmann <aha_1980@gmx.de>

src/plugins/helloworld/helloworldwindow.h

@@ -35,7 +35,7 @@ class HelloWorldWindow : public QWidget
     Q_OBJECT
 
 public:
-    HelloWorldWindow(QWidget *parent = 0);
+    explicit HelloWorldWindow(QWidget *parent = nullptr);
 };
 
 } // namespace Internal