chore: upgrade remaining 2018 edition crates to 2021 edition (#5788)

examples/Cargo.toml

@@ -2,7 +2,7 @@
 name = "examples"
 version = "0.0.0"
 publish = false
-edition = "2018"
+edition = "2021"
 
 # If you copy one of the examples into a new project, you should be using
 # [dependencies] instead, and delete the **path**.

examples/tinyhttp.rs

@@ -18,7 +18,7 @@ use futures::SinkExt;
 use http::{header::HeaderValue, Request, Response, StatusCode};
 #[macro_use]
 extern crate serde_derive;
-use std::{convert::TryFrom, env, error::Error, fmt, io};
+use std::{env, error::Error, fmt, io};
 use tokio::net::{TcpListener, TcpStream};
 use tokio_stream::StreamExt;
 use tokio_util::codec::{Decoder, Encoder, Framed};