chore(readme.md): fix invalid link (#1807)

README.md

@@ -13,7 +13,7 @@
 
 Gin is a web framework written in Go (Golang). It features a martini-like API with much better performance, up to 40 times faster thanks to [httprouter](https://github.com/julienschmidt/httprouter). If you need performance and good productivity, you will love Gin.
 
-![Gin console logger](https://gin-gonic.github.io/gin/other/console.png)
+![Gin console logger](testdata/assets/console.png)
 
 ## Contents