Upgraded to .NET Core 2.0
MODIFY
src/Chapter19/Chapter19.csproj
src/Chapter19/Chapter19.csproj
<Compile Include="..\Shared\PiCalculator+InternalPiDigitCalculator.cs">
<Link>PiCalculator+InternalPiDigitCalculator.cs</Link>
</Compile>
- <Compile Include="..\Shared\AsyncCompletedEventArgs.cs">
- <Link>AsyncCompletedEventArgs.cs</Link>
- </Compile>
<Compile Include="..\Shared\DoWorkEventArgs.cs">
<Link>DoWorkEventArgs.cs</Link>
</Compile>

Upgraded to .NET Core 2.0