Xamarin.Forms-Samples/DependencyServiceSample/packages/repositories.config

<?xml version="1.0" encoding="utf-8"?>
<repositories>
  <repository path="..\DependencyServiceSample\DependencyServiceSample.Droid\packages.config" />
  <repository path="..\DependencyServiceSample\DependencyServiceSample.iOS\packages.config" />
  <repository path="..\DependencyServiceSample\DependencyServiceSample.WinPhone\packages.config" />
  <repository path="..\DependencyServiceSample\DependencyServiceSample\packages.config" />
</repositories>