Update ConsoleTables.nuspec

Change the file target path to "lib\net40\..." for the Nuget package to allow targeting .NET 4.0 projects.

I missed this on my previous pull request, but I think this will also be necessary when you create a new NuGet package or modify the existing one. I think you should be able to have multiple targets, so that it will support several versions of the .NET framework. I am not sure, but I think that .NET 4.5 projects will be able to use packages targets at .NET 4.0, but not vice-versa.