Update README.md

Update nuget package's name

Author: alexinea

README.md

@@ -1,6 +1,6 @@
 # DotnetSpider
 [![Travis branch](https://travis-ci.org/dotnetcore/DotnetSpider.svg?branch=master)](https://travis-ci.org/dotnetcore/DotnetSpider)
-[![NuGet](https://img.shields.io/nuget/v/DotnetSpider2.Extension.svg)](https://www.nuget.org/packages/DotnetSpider2.Extension)
+[![NuGet](https://img.shields.io/nuget/v/DotnetSpider.Extension.svg)](https://www.nuget.org/packages/DotnetSpider.Extension)
 [![Member project of .NET Core Community](https://img.shields.io/badge/member%20project%20of-NCC-9e20c9.svg)](https://github.com/dotnetcore)
 [![GitHub license](https://img.shields.io/aur/license/yaourt.svg)](https://raw.githubusercontent.com/dotnetcore/DotnetSpider/master/LICENSE)