Update to nightly-2020-04-20

tests/ui/missing-display.stderr

@@ -4,5 +4,10 @@ error[E0277]: `MyError` doesn't implement `std::fmt::Display`
 4  | pub enum MyError {
    | ^^^^^^^^^^^^^^^^ `MyError` cannot be formatted with the default formatter
    |
+  ::: $RUST/src/libstd/error.rs
+   |
+   | pub trait Error: Debug + Display {
+   |                          ------- required by this bound in `std::error::Error`
+   |
    = 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