Only reference released versions of ASP.NET Core packages

Author: SteveSandersonMS

NuGet.config

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
 <configuration>
  <packageSources>
- <add key="AspNetCore" value="https://dotnet.myget.org/F/aspnetcore-ci-dev/api/v3/index.json" />
  <add key="AspNetCoreTools" value="https://dotnet.myget.org/F/aspnetcore-tools/api/v3/index.json" />
  <add key="NuGet" value="https://api.nuget.org/v3/index.json" />
  </packageSources>