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

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