Update ui tests to nightly-2020-04-20

Relevant rustc bug: rust-lang/rust#71363

Author: dtolnay

tests/ui/missing-display.stderr

@@ -1,8 +1,8 @@
 error[E0277]: `MyError` doesn't implement `std::fmt::Display`
- --> $DIR/missing-display.rs:4:1
-  |
-4 | pub enum MyError {
-  | ^^^^^^^^^^^^^^^^ `MyError` cannot be formatted with the default formatter
-  |
-  = help: the trait `std::fmt::Display` is not implemented for `MyError`
-  = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+  --> $DIR/missing-display.rs:4:1
+   |
+4  | pub enum MyError {
+   | ^^^^^^^^^^^^^^^^ `MyError` cannot be formatted with the default formatter
+   |
+   = help: the trait `std::fmt::Display` is not implemented for `MyError`
+   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead