[ci skip] update discord badge. (#1930)

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

README.md

@@ -3,7 +3,7 @@
 # Gitea - Git with a cup of tea
 
 [![Build Status](https://drone.gitea.io/api/badges/go-gitea/gitea/status.svg)](https://drone.gitea.io/go-gitea/gitea)
-[![Join the chat at https://gitter.im/go-gitea/gitea](https://badges.gitter.im/Join%20Chat.svg)](https://discord.gg/NsatcWJ)
+[![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)](https://microbadger.com/images/gitea/gitea "Get your own image badge on microbadger.com")
 [![Coverage Status](https://coverage.gitea.io/badges/go-gitea/gitea/coverage.svg)](https://coverage.gitea.io/go-gitea/gitea)
 [![Go Report Card](https://goreportcard.com/badge/code.gitea.io/gitea)](https://goreportcard.com/report/code.gitea.io/gitea)

README_ZH.md

@@ -3,7 +3,7 @@
 # Gitea - Git with a cup of tea
 
 [![Build Status](https://drone.gitea.io/api/badges/go-gitea/gitea/status.svg)](https://drone.gitea.io/go-gitea/gitea)
-[![Join the chat at https://gitter.im/go-gitea/gitea](https://badges.gitter.im/Join%20Chat.svg)](https://discord.gg/NsatcWJ)
+[![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)](https://microbadger.com/images/gitea/gitea "Get your own image badge on microbadger.com")
 [![Coverage Status](https://coverage.gitea.io/badges/go-gitea/gitea/coverage.svg)](https://coverage.gitea.io/go-gitea/gitea)
 [![Go Report Card](https://goreportcard.com/badge/code.gitea.io/gitea)](https://goreportcard.com/report/code.gitea.io/gitea)