More conversion fixes for gcc
diff --git a/include/json/writer.h b/include/json/writer.h
index 180ab68..49b1512 100644
--- a/include/json/writer.h
+++ b/include/json/writer.h
@@ -302,7 +302,7 @@
   ChildValues childValues_;
   std::ostream* document_;
   std::string indentString_;
-  int rightMargin_;
+  unsigned int rightMargin_;
   std::string indentation_;
   bool addChildValues_ : 1;
   bool indented_ : 1;