NuGet Feed Update (dotnet#822)

Co-authored-by: Matt Mitchell <[email protected]>

Author: dotnet-bot

NuGet.config

@@ -2,8 +2,7 @@
 <configuration>
   <packageSources>
     <clear />
-    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
-    <add key="dotnet-core" value="https://dotnetfeed.blob.core.windows.net/dotnet-core/index.json" />
+    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
     <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
     <add key="dotnet-eng" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json" />
     <add key="dotnet5" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet5/nuget/v3/index.json" />