fix incompatibility with .net framework

packages/Avalonia/Avalonia.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-      <PackageReference Include="Avalonia.BuildServices" Version="0.0.27" />
+      <PackageReference Include="Avalonia.BuildServices" Version="0.0.28" />
       <ProjectReference Include="../../src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj" />
       <ProjectReference Include="../../src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj">
         <PrivateAssets>all</PrivateAssets>