Update ui tests to 2018 edition

test_suite/tests/ui/remote/unknown_field.stderr

@@ -1,13 +1,13 @@
 error[E0609]: no field `b` on type `&remote::S`
-  --> $DIR/unknown_field.rs:13:5
+  --> $DIR/unknown_field.rs:12:5
    |
-13 |     b: u8,
+12 |     b: u8,
    |     ^
 
 error[E0560]: struct `remote::S` has no field named `b`
-  --> $DIR/unknown_field.rs:13:5
+  --> $DIR/unknown_field.rs:12:5
    |
-13 |     b: u8,
+12 |     b: u8,
    |     ^ field does not exist - did you mean `a`?
 
 error: aborting due to 2 previous errors