Bump tokio from 0.1.22 to 0.2.4

[dependabot-preview]

Bumps tokio from 0.1.22 to 0.2.4.

Release notes

Sourced from tokio's releases.

Tokio v0.2.4

A small release to fix a potential deadlock when using Mutex.

Fixes

• sync::Mutex deadlock when lock() future is dropped early (#1898).

Tokio v0.2.3

Mostly a bug fix, doc improvement, and polish release. The biggest new addition are the new helpers to read and write integers. They are on AsyncReadExt and AsyncWriteExt and can make protocol encoding / decoding easier. For example, working with length delimited payloads might look like:

use tokio::io::{self, AsyncReadExt, AsyncWriteExt, BufStream};
use tokio::net::TcpStream;

async fn read_frame(src: &mut BufStream<TcpStream>) -> io::Result<Vec<u8>> {
     let len = src.read_u32().await?;
     let mut frame = vec![0; len as usize];
     src.read_exact(&mut frame).await?;

    Ok(frame)
}

async fn write_frame(dst: &mut BufStream<TcpStream>, frame: &[u8]) -> io::Result<()> {
    dst.write_u32(frame.len() as u32).await?;
    dst.write_all(frame).await?;
    dst.flush().await?;

    Ok(())
}

Added

• read / write integers using AsyncReadExt and AsyncWriteExt (#1863).
• read_buf / write_buf for reading / writing Buf / BufMut (#1881).
• TcpStream::poll_peek - pollable API for performing TCP peek (#1864).
• sync::oneshot::error::TryRecvError provides variants to detect the error
  kind (#1874).
• LocalSet::block_on accepts !'static task (#1882).
• task::JoinError is now Sync (#1888).
• impl conversions between tokio::time::Instant and
  std::time::Instant (#1904).

Fixes

• calling spawn_blocking after runtime shutdown (#1875).
• LocalSet drop inifinite loop (#1892).
• LocalSet hang under load (#1905).
• improved documentation (#1865, #1866, #1868, #1874, #1876, #1911).

... (truncated)

Commits

• 80abff0 chore: prepare v0.2.4 release (#1917)
• c632337 sync: fix Mutex when lock future dropped before complete (#1902)
• a53f94a doc: expand on runtime / spawn docs (#1914)
• 98c9a77 prepare v0.2.3 release (#1912)
• e00c496 doc: fix TcpListener example to compile (#1911)
• 9c9fabc Close markdown (#1910)
• c3461b3 time: impl From between std / tokio Instants (#1904)
• b7ecd35 task: fix LocalSet failing to poll all local futures (#1905)
• dbcd1f9 time: Remove HandlePriv (#1896)
• 0e729aa task: fix infinite loop when dropping a LocalSet (#1892)
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #20.