Fix override syntax

Overrides go at the end of the declaration. Qt also has the `Q_DECL_OVERRIDE` preprocessor define, which expands to `override` only when building the code using C++11 or higher.

Author: ferdnyc

include/Qt/PlayerDemo.h

@@ -57,7 +57,7 @@ class PlayerDemo : public QWidget
     ~PlayerDemo();
 
 protected:
-    override void keyPressEvent(QKeyEvent *event);
+    void keyPressEvent(QKeyEvent *event) Q_DECL_OVERRIDE;
     void closeEvent(QCloseEvent *event) Q_DECL_OVERRIDE;
 
 private slots: