Add missing 'override' specifier

This fixes clang warning:
'notify' overrides a member function but is not marked 'override'
[-Winconsistent-missing-override]

src/app/application.h

@@ -112,7 +112,7 @@ protected:
 #ifdef Q_OS_MAC
     bool event(QEvent *);
 #endif
-    bool notify(QObject* receiver, QEvent* event);
+    bool notify(QObject* receiver, QEvent* event) override;
 #endif
 
 private slots:

src/gui/transferlistwidget.h

@@ -110,7 +110,7 @@ protected:
 protected slots:
     void torrentDoubleClicked();
     void displayListMenu(const QPoint&);
-    void currentChanged(const QModelIndex& current, const QModelIndex&);
+    void currentChanged(const QModelIndex& current, const QModelIndex&) override;
     void toggleSelectedTorrentsSuperSeeding() const;
     void toggleSelectedTorrentsSequentialDownload() const;
     void toggleSelectedFirstLastPiecePrio() const;

src/webui/webapplication.h

@@ -88,7 +88,7 @@ public:
     explicit WebApplication(QObject *parent = nullptr);
     ~WebApplication() override;
 
-    Http::Response processRequest(const Http::Request &request, const Http::Environment &env);
+    Http::Response processRequest(const Http::Request &request, const Http::Environment &env) override;
 
     QString clientId() const override;
     WebSession *session() override;