fix warning with unsigned long

src/graph/graph.hh

diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 2b742ef..4942448 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -478,7 +478,7 @@
     for (int i = vertices_.length - 1; i >= 0; i--)
     {
       const auto& v = vertices_[i];
-      printf("%d: %lu [", i, v.table_size());
+      printf("%d: %u [", i, (unsigned int)v.table_size());
       for (const auto &l : v.obj.real_links) {
         printf("%u, ", l.objidx);
       }