Fix build with Qt5-5.14
--- PrintWidget.cpp.orig 2020-04-04 10:57:54 UTC
+++ PrintWidget.cpp
@@ -1,5 +1,6 @@
#include "PrintWidget.h"
#include <QGraphicsProxyWidget>
+#include <QImage>
#include <QPushButton>
#include <QtConcurrent>