nuspec does not match csproj

[jnyrup]

Description

https://www.nuget.org/packages/Microsoft.NET.Test.Sdk/16.3.0
lists netcoreapp1.0 as a target, but the dependency Microsoft.TestPlatform.TestHost 16.3.0 has netcoreapp2.1 as the lowest netcore target.

This seems due to a mismatch between https://github.com/microsoft/vstest/blob/master/src/package/nuspec/Microsoft.NET.Test.Sdk.nuspec
and
https://github.com/microsoft/vstest/blob/master/src/package/package/package.csproj
(and maybe more places?)

Expected behavior

NuGet should list the same target frameworks as the csproj

Actual behavior

NuGet lists netcoreapp1.0, which the csproj does not.

Other

#2067 replaced the netcoreapp1.0 with netcoreapp2.1.
Could it just add the newer target framework instead of replacing the old?