fix: Change README badge from Myget to Nuget (#8)

Signed-off-by: Tan <[email protected]>

Author: Tanyuu

README.md

@@ -3,7 +3,7 @@
 [![Actions Status](https://github.com/casbin-net/redis-watcher/workflows/Build/badge.svg)](https://github.com/casbin-net/redis-watcher/actions)
 [![Coverage Status](https://coveralls.io/repos/github/casbin-net/redis-watcher/badge.svg?branch=master)](https://coveralls.io/github/casbin-net/redis-watcher?branch=master)
 [![License](https://img.shields.io/github/license/casbin-net/redis-watcher)](https://github.com/casbin-net/redis-watcher/blob/master/LICENSE)
-[![Build Version](https://img.shields.io/casbin-net.myget/casbin-net/v/Casbin.Watcher.Redis?label=Casbin.Watcher.Redis)](https://www.myget.org/feed/casbin-net/package/nuget/Casbin.Watcher.Redis)
+[![Nuget](https://img.shields.io/nuget/v/Casbin.Watcher.Redis?label=Casbin.Watcher.Redis)](https://www.nuget.org/packages/Casbin.Watcher.Redis)
 
 Redis watcher for Casbin.NET