Update network-libp2p to edition 2018 (#1481)

substrate/core/network-libp2p/Cargo.toml

@@ -1,5 +1,6 @@
 [package]
 description = "libp2p implementation of the ethcore network library"
+edition = "2018"
 homepage = "http://parity.io"
 license = "GPL-3.0"
 name = "substrate-network-libp2p"
@@ -13,7 +14,6 @@ fnv = "1.0"
 futures = "0.1"
 libp2p = { version = "0.2", default-features = false, features = ["secio-rsa", "secio-secp256k1"] }
 parking_lot = "0.7.1"
-libc = "0.2"
 log = "0.4"
 rand = "0.5.0"
 serde = "1.0.70"
@@ -25,7 +25,3 @@ tokio-io = "0.1"
 tokio-timer = "0.2"
 unsigned-varint = { version = "0.2.1", features = ["codec"] }
 void = "1.0"
-
-[dev-dependencies]
-assert_matches = "1.2"
-parity-bytes = { git = "https://github.com/paritytech/parity-common", rev = "b0317f649ab2c665b7987b8475878fc4d2e1f81d" }