Update ui tests to latest stable (#51)

Author: taiki-e

async-stream/tests/ui/yield_in_async.stderr

@@ -12,7 +12,7 @@ error[E0727]: `async` generators are not yet supported
 6 |             yield 123;
   |             ^^^^^^^^^
 
-error[E0271]: type mismatch resolving `<[static generator@$DIR/src/lib.rs:202:9: 202:67 _] as Generator<ResumeTy>>::Yield == ()`
+error[E0271]: type mismatch resolving `<[static generator@$DIR/src/lib.rs:202:9: 202:67] as Generator<ResumeTy>>::Yield == ()`
   --> $DIR/yield_in_async.rs:4:5
    |
 4  | /     stream! {

async-stream/tests/ui/yield_in_closure.stderr

@@ -6,13 +6,13 @@ error[E0658]: yield syntax is experimental
   |
   = note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
 
-error[E0277]: expected a `FnOnce<(&str,)>` closure, found `[generator@$DIR/src/lib.rs:202:9: 202:67 _]`
+error[E0277]: expected a `FnOnce<(&str,)>` closure, found `[generator@$DIR/src/lib.rs:202:9: 202:67]`
  --> $DIR/yield_in_closure.rs:6:14
   |
 6 |             .and_then(|v| {
-  |              ^^^^^^^^ expected an `FnOnce<(&str,)>` closure, found `[generator@$DIR/src/lib.rs:202:9: 202:67 _]`
+  |              ^^^^^^^^ expected an `FnOnce<(&str,)>` closure, found `[generator@$DIR/src/lib.rs:202:9: 202:67]`
   |
-  = help: the trait `FnOnce<(&str,)>` is not implemented for `[generator@$DIR/src/lib.rs:202:9: 202:67 _]`
+  = help: the trait `FnOnce<(&str,)>` is not implemented for `[generator@$DIR/src/lib.rs:202:9: 202:67]`
 
 Some errors have detailed explanations: E0277, E0658.
 For more information about an error, try `rustc --explain E0277`.