Doc: fix \inmodule for classes moved to QtGui

Change-Id: If7a42dde8c728356e0e5646743a1425b08fccbcb
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

src/gui/itemmodels/qfilesystemmodel.cpp

@@ -74,7 +74,7 @@ QT_BEGIN_NAMESPACE
     \brief The QFileSystemModel class provides a data model for the local filesystem.
 
     \ingroup model-view
-    \inmodule QtWidgets
+    \inmodule QtGui
 
     This class provides access to the local filesystem, providing functions
     for renaming and removing files and directories, and for creating new

src/gui/util/qundogroup.cpp

@@ -57,7 +57,7 @@ public:
     \class QUndoGroup
     \brief The QUndoGroup class is a group of QUndoStack objects.
     \since 4.2
-    \inmodule QtWidgets
+    \inmodule QtGui
 
     For an overview of the Qt's undo framework, see the
     \l{qundo.html}{overview}.

src/gui/util/qundostack.cpp

@@ -51,7 +51,7 @@ QT_BEGIN_NAMESPACE
     \brief The QUndoCommand class is the base class of all commands stored on a QUndoStack.
     \since 4.2
 
-    \inmodule QtWidgets
+    \inmodule QtGui
 
     For an overview of Qt's Undo Framework, see the
     \l{Overview of Qt's Undo Framework}{overview document}.
@@ -347,7 +347,7 @@ const QUndoCommand *QUndoCommand::child(int index) const
     \brief The QUndoStack class is a stack of QUndoCommand objects.
     \since 4.2
 
-    \inmodule QtWidgets
+    \inmodule QtGui
 
     For an overview of Qt's Undo Framework, see the
     \l{Overview of Qt's Undo Framework}{overview document}.