fix NuGet badge to use shields.io

Author: EEParker

README.md

@@ -1,7 +1,7 @@
 # Serilog.Sinks.Splunk
 
 ![Build Status](https://github.com/serilog-contrib/serilog-sinks-splunk/actions/workflows/ci.yml/badge.svg?branch=dev)
-[![NuGet Version](https://buildstats.info/nuget/Serilog.Sinks.Splunk)](https://www.nuget.org/packages/Serilog.Sinks.Splunk)
+[![NuGet Version](https://img.shields.io/nuget/v/Serilog.Sinks.Splunk.svg)](https://www.nuget.org/packages/Serilog.Sinks.Splunk)
 [![Join the chat at https://gitter.im/serilog/serilog](https://img.shields.io/gitter/room/serilog/serilog.svg)](https://gitter.im/serilog/serilog)
 
 A Serilog sink that writes events to the [Splunk](https://splunk.com). Supports .NET 8+, .NET 9, .NET 10, and platforms compatible with the [.NET Platform Standard](https://docs.microsoft.com/en-us/dotnet/standard/net-standard) `netstandard2.0`, `netstandard2.1`.