improve OSX package support

Author: swharden

src/Spectrogram/Spectrogram.csproj

@@ -19,6 +19,7 @@ Quickstart: https://github.com/swharden/Spectrogram</PackageReleaseNotes>
   <ItemGroup>
     <PackageReference Include="FftSharp" Version="1.0.5" />
     <PackageReference Include="System.Drawing.Common" Version="4.7.0" />
+    <PackageReference Include="runtime.osx.10.10-x64.CoreCompat.System.Drawing" Version="5.8.64" Condition="'$([System.Runtime.InteropServices.RuntimeInformation]::IsOSPlatform($([System.Runtime.InteropServices.OSPlatform]::OSX)))' == 'true'" />
   </ItemGroup>
 
   <ItemGroup>