Set episode file modified date to local or utc air date

src/Microsoft.AspNet.SignalR.Core/Microsoft.AspNet.SignalR.Core.csproj

@@ -275,6 +275,7 @@
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">
   </Target>
+  <Import Project="$(SolutionDir)\.nuget\NuGet.targets" Condition="Exists('$(SolutionDir)\.nuget\NuGet.targets')" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">