Merge pull request #3489 from LeoHChen/libp2p_upgrade

[go.mod] libp2p upgrade

go.mod

@@ -31,8 +31,8 @@ require (
 	github.com/harmony-one/vdf v0.0.0-20190924175951-620379da8849
 	github.com/hashicorp/golang-lru v0.5.4
 	github.com/ipfs/go-ds-badger v0.2.4
-	github.com/libp2p/go-libp2p v0.12.0
-	github.com/libp2p/go-libp2p-core v0.7.0
+	github.com/libp2p/go-libp2p v0.13.0
+	github.com/libp2p/go-libp2p-core v0.8.0
 	github.com/libp2p/go-libp2p-crypto v0.1.0
 	github.com/libp2p/go-libp2p-discovery v0.5.0
 	github.com/libp2p/go-libp2p-kad-dht v0.11.1