Fix filename in header comment

src/commands/exportpaperkeycommand.h

 /* -*- mode: c++; c-basic-offset:4 -*-
-    commands/exportsecretkeycommand.h
+    commands/exportpaperkeycommand.h
 
     This file is part of Kleopatra, the KDE keymanager
     SPDX-FileCopyrightText: 2016 Bundesamt für Sicherheit in der Informationstechnik