deps: update libp2p requirement from 0.51 to 0.52

Updates the requirements on [libp2p](https://github.com/libp2p/rust-libp2p) to permit the latest version.
- [Release notes](https://github.com/libp2p/rust-libp2p/releases)
- [Changelog](https://github.com/libp2p/rust-libp2p/blob/master/CHANGELOG.md)
- [Commits](libp2p/rust-libp2p@v0.51.0...libp2p-v0.51.3)

---
updated-dependencies:
- dependency-name: libp2p
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Cargo.toml

@@ -18,7 +18,7 @@ tokio-crate = { package = "tokio", version = "1", optional = true, default-featu
 tor-rtcompat = "0.8"
 
 [dev-dependencies]
-libp2p = { version = "0.51", features = ["mplex", "noise", "ping", "yamux", "macros", "async-std"] }
+libp2p = { version = "0.52", features = ["mplex", "noise", "ping", "yamux", "macros", "async-std"] }
 tokio-crate = { package = "tokio", version = "1", features = ["rt", "macros"] }
 async-std-crate = { package = "async-std", version = "1", features = ["attributes"] }