added missing #include

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403751

dlib/rand/mersenne_twister.h

@@ -20,6 +20,7 @@
 #include <algorithm>     // std::copy
 #include <stdexcept>
 #include "../uintn.h"
+#include "../serialize.h"
 
 namespace dlib 
 {