Add seemingly missing string includes.

code/compiler/10/type.hpp

@@ -1,6 +1,7 @@
 #pragma once
 #include <memory>
 #include <map>
+#include <string>
 #include <vector>
 #include <set>
 

code/compiler/10/type_env.hpp

@@ -1,5 +1,6 @@
 #pragma once
 #include <map>
+#include <string>
 #include "type.hpp"
 
 struct type_env;