chore: remove gitter badge from README

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Co-Authored-By: Claude <[email protected]>

Author: appleboy

README.md

@@ -5,7 +5,6 @@
 [![codecov](https://codecov.io/gh/gin-contrib/httpsign/branch/master/graph/badge.svg)](https://codecov.io/gh/gin-contrib/httpsign)
 [![Go Report Card](https://goreportcard.com/badge/github.com/gin-contrib/httpsign)](https://goreportcard.com/report/github.com/gin-contrib/httpsign)
 [![GoDoc](https://godoc.org/github.com/gin-contrib/httpsign?status.svg)](https://godoc.org/github.com/gin-contrib/httpsign)
-[![Join the chat at https://gitter.im/gin-gonic/gin](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/gin-gonic/gin)
 
 Signing HTTP Messages Middleware base on [HTTP Signatures](https://tools.ietf.org/html/draft-cavage-http-signatures).