qt: mark eventFilter as 'override' to match virtual func

Should take care of this:

In file included from qt/moc_signverifymessagedialog.cpp:8:
./qt/signverifymessagedialog.h:36:10: warning: 'eventFilter' overrides a member function but is not marked 'override'
      [-Winconsistent-missing-override]
    bool eventFilter(QObject *object, QEvent *event);
         ^
/Users/localhost/Projects/dash/depends/x86_64-apple-darwin18.7.0/include/QtWidgets/qdialog.h:111:10: note: overridden virtual function is here
    bool eventFilter(QObject *, QEvent *) override;
         ^

Author: kwvg

src/qt/signverifymessagedialog.h

@@ -33,7 +33,7 @@ class SignVerifyMessageDialog : public QDialog
     void showTab_VM(bool fShow);
 
 protected:
-    bool eventFilter(QObject *object, QEvent *event);
+    bool eventFilter(QObject *object, QEvent *event) override;
 
 private:
     Ui::SignVerifyMessageDialog *ui;