QmlDesigner: Compile fix

Change-Id: I0d8e37253f472270b8efbc433dc2664f28a2b6b4
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
Reviewed-by: Nikita Baryshnikov <nib952051@gmail.com>

src/plugins/qmldesigner/components/propertyeditor/gradientmodel.h

@@ -33,6 +33,7 @@
 #include <qmlitemnode.h>
 
 #include <QAbstractListModel>
+#include <QColor>
 #include <QtQml>
 
 class GradientModel : public QAbstractListModel