How to use latest dot net core in Universal Windows Class Library?

I would like to use the latest .NET Core in a new Universal Windows Class Library.

However creating a new library in VS2015 the System.Net.Sockets.Socket API does not appear to be updated. In particular I want this commit: https://github.com/dotnet/corefx/pull/4079/files

My project.json looks like:

{
  "dependencies": {
    "Microsoft.NETCore.UniversalWindowsPlatform": "5.0.0"
  },
  "frameworks": {
    "uap10.0": {}
  },
  "runtimes": {
    "win10-arm": {},
    "win10-arm-aot": {},
    "win10-x86": {},
    "win10-x86-aot": {},
    "win10-x64": {},
    "win10-x64-aot": {}
  }
}