fix error

ch11/ex11_9_10.cpp

@@ -9,7 +9,7 @@
 //! to int? What about from list<int>::iterator to int?
 //! In each case, if not, why not?
 //  vector<int>::iterator to int is ok ,because < is defined
-//  vector<int>::iterator to int is not ok,as no < is defined.
+//  list<int>::iterator to int is not ok,as no < is defined.
 #include <iostream>
 #include <map>
 #include <string>