Fixed code example (#2955)

docs/frequently-asked-questions.rst

@@ -432,12 +432,12 @@ What happens to a ``struct``'s mapping when copying over a ``struct``?
 This is a very interesting question. Suppose that we have a contract field set up like such::
 
     struct user {
-        mapping(string => address) usedContracts;
+        mapping(string => string) comments;
     }
 
     function somefunction {
        user user1;
-       user1.usedContracts["Hello"] = "World";
+       user1.comments["Hello"] = "World";
        user user2 = user1;
     }