NuGet version needs to be updated on Jenkins machines running 'Full Framework'

[johnbeisner]

The SDK unit test: Microsoft.NET.Build.Tests.GivenThatWeWantToVerifyProjectReferenceCompat
has 6 permutations that are failing because Jenkins machines running 'Full Framework' are using an older version of NuGet:
net461 referencing netstandard1.5
net461 referencing netstandard1.6
net461 referencing netstandard2.0
net462 referencing netstandard1.6
net462 referencing netstandard2.0
netcoreapp2.0 referencing netstandard2.0

Once NuGet is updated, the unit tests should be updated as well...