CppEditor: build fix (Qt5)

Change-Id: I8771ee574f9b2d0cd78786f6cd7c2e19d8865412
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/cppeditor/cppinsertvirtualmethods.cpp

@@ -53,6 +53,7 @@
 #include <QStandardItemModel>
 #include <QTextDocument>
 #include <QTreeView>
+#include <QVBoxLayout>
 
 using namespace CPlusPlus;
 using namespace CppEditor;