docs(examples): updated imports in client_json example (#2412)

examples/client_json.rs

@@ -1,11 +1,9 @@
 #![deny(warnings)]
 #![warn(rust_2018_idioms)]
 
-#[macro_use]
-extern crate serde_derive;
-
-use bytes::Buf as _;
+use hyper::body::Buf;
 use hyper::Client;
+use serde::Deserialize;
 
 // A simple type alias so as to DRY.
 type Result<T> = std::result::Result<T, Box<dyn std::error::Error + Send + Sync>>;