[LyX/2.3-staging] Fix compilation with qt5

[Guillaume Munch]

commit 01bcaf59e9814fbe7443f9829df6dc7a07c99544
Author: Guillaume Munch <g...@lyx.org>
Date:   Sun Apr 17 14:21:43 2016 +0100

    Fix compilation with qt5
    
    Amend 367a7a6d.

diff --git a/src/frontends/qt4/LyXToolBox.h b/src/frontends/qt4/LyXToolBox.h
index ec70ceb..03bd00e 100644
--- a/src/frontends/qt4/LyXToolBox.h
+++ b/src/frontends/qt4/LyXToolBox.h
@@ -12,7 +12,7 @@
 #ifndef LYXTOOLBOX_H
 #define LYXTOOLBOX_H
 
-#include <QtGui/QToolBox>
+#include <QToolBox>
 
 namespace lyx {
 namespace frontend {