SDWebImage crash

Hello all!

I've just tried SDWebImage library from xamarin components and get a crash.

Here is the code

    imageViewUserPhoto.SetImage(
       url: new NSUrl ("some url"), 
       placeholder: UIImage.FromBundle ("placeholder.png")
    );

and the crash log:

System.TypeLoadException: Could not load type 'System.Runtime.CompilerServices.ExtensionAttribute' from assembly 'SDWebImage'.

Can somebody help me with it?