docs: deal with Result instead of using unwrap
//! use bytes::Bytes;
//! use futures::{Sink, Future};
//!
-//! fn write_frame<T: AsyncRead + AsyncWrite>(io: T) {
+//! fn write_frame<T: AsyncRead + AsyncWrite>(io: T) -> Result<(), Box<std::error::Error>> {
//! let mut transport = Framed::new(io, LengthDelimitedCodec::new());
//! let frame = Bytes::from("hello world");
//!
-//! transport.send(frame).wait().unwrap();
+//! transport.send(frame).wait()?;
+//! Ok(())
//! }
//! #
//! # pub fn main() {}
