vcmi: bump serializer version

lib/serializer/CSerializer.h

@@ -14,8 +14,8 @@
 
 VCMI_LIB_NAMESPACE_BEGIN
 
-const ui32 SERIALIZATION_VERSION = 820;
-const ui32 MINIMAL_SERIALIZATION_VERSION = 820;
+const ui32 SERIALIZATION_VERSION = 821;
+const ui32 MINIMAL_SERIALIZATION_VERSION = 821;
 const std::string SAVEGAME_MAGIC = "VCMISVG";
 
 class CHero;