Update nuget packages to current versions of everything

@robmoore (or someone else familiar with NSubstitute / AutofacContrib.NSubstitute), would you mind please having a look at fc607a8d784a26e734ac3e46924765e358b7cc15 where I've deleted the line: `SUT.SelectedElementAs<ChoiceType>().Returns(ChoiceType.Another);`
This line was causing an exception because SelectedElementAs calls IWebElement.GetAttribute() which triggers the last call in NSubstitute. I think the later line: `...GetAttribute().Returns(ChoiceType.Another.ToString())` is sufficient to set the object up correctly, but I wasn't sure that I understood the intent correctly.

All tests passing locally and nuspec updated correctly. Is it safe to assume that version tagging etc. is done by the CI server?