title: Nuget package installation failed in VS 2017 (.net core)
body: <p>I created new Console App(.NET Core) and i am trying to add package with NuGet 
  the package is : Microsoft.Extensions.Configuration
  When I click install I get this message:</p>
  
  <pre><code>Package restore failed. Rolling back package changes for 'ConsoleApp1'.
  </code></pre>