Update ui tests to 2018 edition

test_suite/tests/ui/default-attribute/nameless_struct_fields_path.stderr

@@ -1,7 +1,7 @@
 error: #[serde(default = "...")] can only be used on structs with named fields
- --> $DIR/nameless_struct_fields_path.rs:6:9
+ --> $DIR/nameless_struct_fields_path.rs:5:9
   |
-6 | struct T(u8, u8);
+5 | struct T(u8, u8);
   |         ^^^^^^^^
 
 error: aborting due to previous error