Bump rust-version to 1.39

Forgot to do this after #27

Author: notgull

Cargo.toml

@@ -6,7 +6,7 @@ name = "event-listener"
 version = "2.5.3"
 authors = ["Stjepan Glavina <[email protected]>"]
 edition = "2018"
-rust-version = "1.36"
+rust-version = "1.39"
 description = "Notify async tasks or threads"
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/smol-rs/event-listener"