Update ui tests to 2018 edition

test_suite/tests/ui/identifier/not_unit.stderr

@@ -1,8 +1,8 @@
 error: #[serde(other)] must be on a unit variant
- --> $DIR/not_unit.rs:8:5
+ --> $DIR/not_unit.rs:7:5
   |
-8 | /     #[serde(other)]
-9 | |     Other(u8, u8),
+7 | /     #[serde(other)]
+8 | |     Other(u8, u8),
   | |_________________^
 
 error: aborting due to previous error