Version bump to v0.3.1 (#203)

Author: AgeManning

Cargo.toml

@@ -2,7 +2,7 @@
 name = "discv5"
 authors = ["Age Manning <[email protected]>"]
 edition = "2018"
-version = "0.3.0"
+version = "0.3.1"
 description = "Implementation of the p2p discv5 discovery protocol"
 license = "Apache-2.0"
 repository = "https://github.com/sigp/discv5"
@@ -12,7 +12,7 @@ categories = ["network-programming", "asynchronous"]
 exclude = [".gitignore", ".github/*"]
 
 [dependencies]
-enr = { version = "0.8.1", features = ["k256", "ed25519"] }
+enr = { version = "0.9.0", features = ["k256", "ed25519"] }
 tokio = { version = "1.15.0", features = ["net", "sync", "macros", "rt"] }
 libp2p-core = { version = "0.40.0", optional = true }
 libp2p-identity = { version = "0.2.1", features = ["ed25519", "secp256k1"], optional = true }