message: docs(client): update client example to use to_bytes
diff: //! println!("status: {}", res.status());
  //!
  //! // Concatenate the body stream into a single buffer...
  -//! let mut body = res.into_body();
  -//! let mut bytes = Vec::new();
  -//! while let Some(next) = body.data().await {
  -//! let chunk = next?;
  -//! bytes.extend(chunk);
  -//! }
  +//! let buf = hyper::body::to_bytes(res.into_body()).await?;
  //!
  -//! // And then, if reading the full body succeeds...
  -//! // The body is just bytes, but let's print a string...
  -//! let s = std::str::from_utf8(&bytes)
  -//! .expect("httpbin sends utf-8 JSON");
  -//!
  -//! println!("body: {}", s);
  +//! println!("body: {:?}", buf);
  //! # Ok(())
  //! # }
  //! # fn main () {}
  