svg-flatten: Fix compilation on recent gcc

svg-flatten/src/nopencv.cpp

@@ -1,4 +1,5 @@
 
+#include <cstdint>
 #include <iostream>
 #include <iomanip>
 #include <stack>

svg-flatten/src/out_dilater.cpp

@@ -25,6 +25,7 @@
 #include <clipper.hpp>
 #include <svg_import_defs.h>
 #include <svg_geom.h>
+#include <cstdint>
 #include "polylinecombine.hpp"
 
 using namespace gerbolyze;

svg-flatten/src/out_flattener.cpp

@@ -24,6 +24,7 @@
 #include <gerbolyze.hpp>
 #include <svg_import_defs.h>
 #include <svg_geom.h>
+#include <cstdint>
 #include "polylinecombine.hpp"
 
 using namespace gerbolyze;