add nuget preview bagdes.

README.zh-cn.md

@@ -5,7 +5,8 @@
 # CAP 　　　　　　　　　　　　　　　　　　　　　　
 [![Travis branch](https://img.shields.io/travis/dotnetcore/CAP/master.svg?label=travis-ci)](https://travis-ci.org/dotnetcore/CAP)
 [![AppVeyor](https://ci.appveyor.com/api/projects/status/4mpe0tbu7n126vyw?svg=true)](https://ci.appveyor.com/project/yuleyule66/cap)
-[![NuGet](https://img.shields.io/nuget/vpre/DotNetCore.CAP.svg)](https://www.nuget.org/packages/DotNetCore.CAP/)
+[![NuGet](https://img.shields.io/nuget/v/DotNetCore.CAP.svg)](https://www.nuget.org/packages/DotNetCore.CAP/)
+[![NuGet Preview](https://img.shields.io/nuget/vpre/DotNetCore.CAP.svg?label=nuget-pre)](https://www.nuget.org/packages/DotNetCore.CAP/)
 [![Member Project Of .NET China Foundation](https://github.com/dotnetcore/Home/raw/master/icons/member-project-of-netchina.png)](https://github.com/dotnetcore)
 [![GitHub license](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/dotnetcore/CAP/master/LICENSE.txt)