Updated IsMvcProject to detect PackageReferences from newer NuGet versions

[declspec]

This resolves #173

Please note: this was just a quick solution I came up with, happy to discuss actual implementation details.

A better solution would be to properly parse the csproj/vbproj files with XML/XPath, but this may be classified as a backwards incompatible change.

It would match the intent of the current implementation, but not match the actual implementation. For example, at the moment you can put an XML comment with <!-- System.Web.Mvc, Version=5 --> to get around the PackageReference issue, this would not work with XPath.