docs: add sourcegraph badge.

README.md

@@ -1,6 +1,6 @@
 # JWT Middleware for Gin Framework
 
-[![GitHub tag](https://img.shields.io/github/tag/appleboy/gin-jwt.svg)](https://github.com/appleboy/gin-jwt/releases) [![GoDoc](https://godoc.org/github.com/appleboy/gin-jwt?status.svg)](https://godoc.org/github.com/appleboy/gin-jwt)  [![Build Status](http://drone.wu-boy.com/api/badges/appleboy/gin-jwt/status.svg)](http://drone.wu-boy.com/appleboy/gin-jwt) [![Go Report Card](https://goreportcard.com/badge/github.com/appleboy/gin-jwt)](https://goreportcard.com/report/github.com/appleboy/gin-jwt) [![codecov](https://codecov.io/gh/appleboy/gin-jwt/branch/master/graph/badge.svg)](https://codecov.io/gh/appleboy/gin-jwt) [![codebeat badge](https://codebeat.co/badges/c4015f07-df23-4c7c-95ba-9193a12e14b1)](https://codebeat.co/projects/github-com-appleboy-gin-jwt) [![license](http://img.shields.io/badge/license-MIT-red.svg?style=flat)](https://raw.githubusercontent.com/appleboy/gin-jwt/master/LICENSE)
+[![GitHub tag](https://img.shields.io/github/tag/appleboy/gin-jwt.svg)](https://github.com/appleboy/gin-jwt/releases) [![GoDoc](https://godoc.org/github.com/appleboy/gin-jwt?status.svg)](https://godoc.org/github.com/appleboy/gin-jwt)  [![Build Status](http://drone.wu-boy.com/api/badges/appleboy/gin-jwt/status.svg)](http://drone.wu-boy.com/appleboy/gin-jwt) [![Go Report Card](https://goreportcard.com/badge/github.com/appleboy/gin-jwt)](https://goreportcard.com/report/github.com/appleboy/gin-jwt) [![codecov](https://codecov.io/gh/appleboy/gin-jwt/branch/master/graph/badge.svg)](https://codecov.io/gh/appleboy/gin-jwt) [![codebeat badge](https://codebeat.co/badges/c4015f07-df23-4c7c-95ba-9193a12e14b1)](https://codebeat.co/projects/github-com-appleboy-gin-jwt) [![Sourcegraph](https://sourcegraph.com/github.com/appleboy/gin-jwt/-/badge.svg)](https://sourcegraph.com/github.com/appleboy/gin-jwt?badge)
 
 This is a middleware for [Gin](https://github.com/gin-gonic/gin) framework.