Fix a typo in ReducedStateInfo

It happened to work by accident because Score and
Value are both integer.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/position.cpp

@@ -671,7 +671,7 @@ void Position::do_move(Move m, StateInfo& newSt, const CheckInfo& ci, bool moveI
     Key pawnKey, materialKey;
     int castleRights, rule50, pliesFromNull;
     Square epSquare;
-    Value value;
+    Score value;
     Value npMaterial[2];
   };