replace gitter chat with discord. (#60)

README.md

@@ -1,7 +1,7 @@
 # Gitea SDK for Go
 
 [![Build Status](http://drone.gitea.io/api/badges/go-gitea/go-sdk/status.svg)](http://drone.gitea.io/go-gitea/go-sdk)
-[![Join the chat at https://gitter.im/go-gitea/gitea](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/go-gitea/gitea?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Join the chat at https://img.shields.io/discord/322538954119184384.svg](https://img.shields.io/discord/322538954119184384.svg)](https://discord.gg/NsatcWJ)
 [![](https://images.microbadger.com/badges/image/gitea/gitea.svg)](http://microbadger.com/images/gitea/gitea "Get your own image badge on microbadger.com")
 [![Coverage Status](https://coverage.gitea.io/badges/go-gitea/go-sdk/coverage.svg)](https://coverage.gitea.io/go-gitea/go-sdk)
 [![Go Report Card](https://goreportcard.com/badge/code.gitea.io/sdk)](https://goreportcard.com/report/code.gitea.io/sdk)