fix: include visit.hpp from serializer

toml.hpp

@@ -37,6 +37,5 @@
 #include "toml/literal.hpp"
 #include "toml/serializer.hpp"
 #include "toml/get.hpp"
-#include "toml/visit.hpp"
 
 #endif// TOML_FOR_MODERN_CPP

toml/serializer.hpp

@@ -4,6 +4,7 @@
 #define TOML11_SERIALIZER_HPP
 #include "value.hpp"
 #include "lexer.hpp"
+#include "visit.hpp"
 #include <limits>
 #include <cstdio>