README: NuGet badge from shields.io, buildstats.info is gone

Author: Astn

README.md

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 # JSON-RPC.Net
 
-![Build Master](https://github.com/Astn/JSON-RPC.NET/workflows/Build%20Master/badge.svg) ![NuGet Badge](https://buildstats.info/nuget/AustinHarris.JsonRpc)
+![Build Master](https://github.com/Astn/JSON-RPC.NET/workflows/Build%20Master/badge.svg) ![NuGet](https://img.shields.io/nuget/v/AustinHarris.JsonRpc)
 
 JSON-RPC.Net is a [JSON-RPC 2.0](https://www.jsonrpc.org/specification) server for .NET. You give it a request document and it gives you the response document, bytes in and bytes out; the transport is yours. Host it in Kestrel, a console app, sockets, pipes, or a Blazor WebAssembly page.