Class Library (Portable) UWP + WPF

Question

I created a simple project Portable Class Library that is being used in two projects WPF e UWP.

The two projects work normally, however, the project UWP when compiling displays the following error message:

Although the project works normally intrigued me this message, someone would know the reason?

project.json

{
  "supports": {
    "net46.app": {},
    "uwp.10.0.app": {}
  },
  "dependencies": {
    "Microsoft.NETCore.Portable.Compatibility": "1.0.1",
    "NETStandard.Library": "1.6.0"
  },
  "frameworks": {
    ".NETStandard1.3": {}
  }
}

Answer 1

The problem was Microsoft.NETCore.UniversalWindowsPlatform outdated in the project WUP, was just looking for update via Nuget and the problem was solved.

Nothing like visiting the Nuget from time to time to solve some problems.

See the before and after: