Bump to 2021 edition

Author: jtgeibel

Cargo.toml

@@ -6,8 +6,8 @@ license = "MIT OR Apache-2.0"
 description = "Host a conduit based web application on a hyper server"
 repository = "https://github.com/jtgeibel/conduit-hyper"
 readme = "README.md"
-edition = "2018"
-rust-version = "1.46.0"
+edition = "2021"
+rust-version = "1.56.0"
 
 [dependencies]
 bytes = "1"