Update NuGet.Config

NuGet.Config

@@ -3,8 +3,6 @@
   <packageSources>
     <clear />
     <add key="api.nuget.org" value="https://api.nuget.org/v3/index.json" />
-    <add key="avalonia-ci" value="https://www.myget.org/F/avalonia-ci/api/v2" />
-    <add key="avalonia-prs" value="https://www.myget.org/F/avalonia-prs/api/v3/index.json" />
-    <add key="dotnet-core" value="https://dotnetfeed.blob.core.windows.net/dotnet-core/index.json" />
+    <add key="avalonia" value="https://nuget.avaloniaui.net/repository/avalonia-all/index.json" protocolVersion="3" />
   </packageSources>
 </configuration>