A new version of the NuGet addin for Xamarin Studio and MonoDevelop has been released.
New Features
The main change is to include NuGet 2.8.1 which adds support for Windows Phone 8.1 projects. Also some of the newer NuGet packages, such as Microsoft.Bcl.Immutable 1.1.20-beta, which the Roslyn NuGet packages depend on, will not install unless NuGet 2.8.1 is being used.
For a detailed look at the changes please read the release note.