README: Change gitter badge to discord

README.md

@@ -7,7 +7,7 @@ https://camo.githubusercontent.com/915b7be44ada53c290eb157634330494ebe3e30a/6874
 )](https://godoc.org/github.com/ethereum/go-ethereum)
 [![Go Report Card](https://goreportcard.com/badge/github.com/ethereum/go-ethereum)](https://goreportcard.com/report/github.com/ethereum/go-ethereum)
 [![Travis](https://travis-ci.org/ethereum/go-ethereum.svg?branch=master)](https://travis-ci.org/ethereum/go-ethereum)
-[![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/ethereum/go-ethereum?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
+[![Discord](https://img.shields.io/badge/discord-join%20chat-blue.svg)](https://discord.gg/nthXNEv)
 
 Automated builds are available for stable releases and the unstable master branch.
 Binary archives are published at https://geth.ethereum.org/downloads/.