[ci skip] update gin gitter link.

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

README.md

@@ -4,7 +4,7 @@
 [![codecov](https://codecov.io/gh/gin-contrib/cors/branch/master/graph/badge.svg)](https://codecov.io/gh/gin-contrib/cors)
 [![Go Report Card](https://goreportcard.com/badge/github.com/gin-contrib/cors)](https://goreportcard.com/report/github.com/gin-contrib/cors)
 [![GoDoc](https://godoc.org/github.com/gin-contrib/cors?status.svg)](https://godoc.org/github.com/gin-contrib/cors)
-[![Join the chat at https://gitter.im/gin-gonic/gin](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/gin-gonic/gin?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![Join the chat at https://gitter.im/gin-gonic/gin](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/gin-gonic/gin)
 
 Gin middleware/handler to enable CORS support.