*: 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/behaviour.rs

@@ -3251,7 +3251,7 @@ impl fmt::Debug for PublishConfig {
 mod local_test {
     use super::*;
     use crate::IdentTopic;
-    use futures_codec::Encoder;
+    use asynchronous_codec::Encoder;
     use quickcheck::*;
     use rand::Rng;