Update ui tests to 2018 edition

test_suite/tests/ui/transparent/de_at_least_one.stderr

@@ -1,13 +1,13 @@
 error: #[serde(transparent)] requires at least one field that is neither skipped nor has a default
-  --> $DIR/de_at_least_one.rs:5:1
+  --> $DIR/de_at_least_one.rs:4:1
    |
-5  | / #[serde(transparent)]
-6  | | struct S {
-7  | |     #[serde(skip)]
-8  | |     a: u8,
-9  | |     #[serde(default)]
-10 | |     b: u8,
-11 | | }
+4  | / #[serde(transparent)]
+5  | | struct S {
+6  | |     #[serde(skip)]
+7  | |     a: u8,
+8  | |     #[serde(default)]
+9  | |     b: u8,
+10 | | }
    | |_^
 
 error: aborting due to previous error