prepend version source file to compile file list

[ctaggart]

fix #308. Code from there too, except for one $ to a @.

Tested locally by modifying in place:
"C:\Users\taggac.nuget\packages\nerdbank.gitversioning\2.3.136\build\Nerdbank.GitVersioning.targets"

    <Message Text="Compile Items Before" Importance="high" />
    <Message Text="@(Compile)" Importance="high" />
    <ItemGroup>
      <_CompileWithVersionFile Include="$(VersionSourceFile);@(Compile)" />
      <Compile Remove="@(Compile)" />
      <Compile Include="@(_CompileWithVersionFile)" />
      <_CompileWithVersionFile Remove="@(_CompileWithVersionFile)" />
    </ItemGroup>
    <Message Text="Compile Items After" Importance="high" />
    <Message Text="@(Compile)" Importance="high" />

Everything compile correctly and I saw this like I was expecting:

       GenerateAssemblyVersionInfo:
         Compile Items Before
         Ast.fs;Parser.fs;ClassModel.fs
         Compile Items After
         obj\Debug\netstandard2.0\\Froto.Parser.Version.fs;Ast.fs;Parser.fs;ClassModel.fs

   1:2>Project "C:\Users\taggac\github\froto\Froto.sln" (1:2) is building "C:\Users\taggac\github\froto\Compiler\Froto.Compiler.fsproj" (3:6) on node 5 (default targets).
     3>GetBuildVersion:
         Building version 0.6.4.62844 from commit 7cf54c4eb8adb025047f63f74f72db2b9204a8c0
       GenerateAssemblyVersionInfo:
         Compile Items Before
         Program.fs
         Compile Items After
         obj\Debug\netcoreapp2.1\\Froto.Compiler.Version.fs;Program.fs

[AArnott]

Thanks for catching my bug and fixing this, and testing it!