Update to 2021 edition

Signed-off-by: John Nunley <[email protected]>

Author: notgull

Cargo.toml

@@ -5,7 +5,7 @@ name = "async-executor"
 # - Create "v1.x.y" git tag
 version = "1.7.1"
 authors = ["Stjepan Glavina <[email protected]>"]
-edition = "2018"
+edition = "2021"
 rust-version = "1.61"
 description = "Async executor"
 license = "Apache-2.0 OR MIT"