Result needs to be fully qualified

Without this:

```
error[E0244]: wrong number of type arguments
  --> src/api/accounts.rs:19:10
   |
19 | #[derive(Serialize, Deserialize, Debug)]
   |          ^^^^^^^^^^ expected 1 type arguments, found 2
```

serde_codegen/src/ser.rs

@@ -636,7 +636,7 @@ fn wrap_serialize_with(
         }
 
         impl $wrapper_generics _serde::ser::Serialize for $wrapper_ty $where_clause {
-            fn serialize<__S>(&self, __s: &mut __S) -> Result<(), __S::Error>
+            fn serialize<__S>(&self, __s: &mut __S) -> ::std::result::Result<(), __S::Error>
                 where __S: _serde::ser::Serializer
             {
                 $path(self.value, __s)