Included cstddef to stream.h

src/stream.h

@@ -6,11 +6,12 @@
 
 #include "yaml-cpp/noncopyable.h"
 #include "yaml-cpp/mark.h"
+#include <cstddef>
 #include <deque>
 #include <ios>
-#include <string>
 #include <iostream>
 #include <set>
+#include <string>
 
 namespace YAML
 {