update readme

Author: macrozheng

README.md

@@ -19,7 +19,7 @@
 
 > 前台商城系统
 
-![前台商城系统功能演示.gif](https://github.com/macrozheng/mall/blob/master/document/resource/mall-app.gif])
+![前台商城系统功能演示.gif](https://github.com/macrozheng/mall/blob/master/document/resource/mall-app.gif)
 
 ### 组织结构