*: Switch futures_codec to asynchronous-codec (#1908)

`futures-codec` has not been updated in the recent months. It still
depends on `bytes` `v0.5` preventing all downstream dependencies to
upgrade to `bytes` `v1.0`.

This commit replaces `futures_codec` in favor of `asynchronous-codec`
The latter is a fully upgraded fork of the former.

In addition this commit upgrades:

- bytes to v1
- unsigned-varint to v0.6.0
- prost to v0.7

protocols/gossipsub/src/protocol.rs

@@ -32,7 +32,7 @@ use bytes::Bytes;
 use bytes::BytesMut;
 use futures::future;
 use futures::prelude::*;
-use futures_codec::{Decoder, Encoder, Framed};
+use asynchronous_codec::{Decoder, Encoder, Framed};
 use libp2p_core::{
     identity::PublicKey, InboundUpgrade, OutboundUpgrade, PeerId, ProtocolName, UpgradeInfo,
 };