[You need to increase the $(TargetFrameworkVersion) for your project] warning

After upgrading Visual Studio 2017 to version 15.8, my android project is getting the following warning:

The $(TargetFrameworkVersion) for App3.Android.dll (v9.0) is greater than the $(TargetFrameworkVersion) for your project (v8.1). You need to increase the $(TargetFrameworkVersion) for your project

To reproduce this error:
1. Create a new "Mobile App (Xamarin.Forms)" project with Code Sharing Strategy using ".NET Standard"
2. Build the project

In my project's Properties->Application, Compile using Android version: Android 8.1 (Oreo)
And in my Android Manaifest, Target Android version: Android 8.1 (API Level 27-Oreo)
And in my project csproj, AndroidUseLatestPlatformSdk is set to false

Anyone encountered this warning?