Update ui tests to nightly-2020-07-15

Author: dtolnay

tests/ui/self-span.stderr

@@ -5,7 +5,7 @@ error[E0423]: expected value, found struct `S`
    | --------------- `S` defined here
 ...
 18 |         let _: Self = Self;
-   |                       ^^^^ did you mean `S { /* fields */ }`?
+   |                       ^^^^ help: use struct literal syntax instead: `S {}`
 
 error[E0308]: mismatched types
   --> $DIR/self-span.rs:17:21