upgrade Rust 2021 edition

bnusunny · bnusunny · commit 0f073dde6c1d · 2022-07-18T12:34:40.000+08:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -2,7 +2,7 @@
 name = "aws-lambda-adapter"
 version = "0.3.2"
 authors = ["Harold Sun <sunhua@amazon.com>"]
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 env_logger = "0.8.3"
