Error adding log4net to a Xamarin Forms solution

I get the following error when I try to add log4net from Nuget.

Adding log4net...
Adding 'log4net 2.0.4' to FiberChekMOBILE.iOS.
Could not install package 'log4net 2.0.4'. You are trying to install this package into a project that targets 'Xamarin.iOS,Version=v1.0', but the package does not contain any assembly references or content files that are compatible with that framework. For more information, contact the package author.

What version of the Xamarin.iOS should I be using to get log4net?