NuGet install-package failing : <p>I'm attempting to install xunit version 2.1.0.. However I'm getting the following exception:</p>

<p>Install-Package : Exception 'System.AggregateException' thrown when trying to add source '<a href="https://api.nuget.org/v3/index.json" rel="noreferrer">https://api.nuget.org/v3/index.json</a>'. Please verify all your o
nline package sources are available.
At line:1 char:16
+ Install-Package &lt;&lt;&lt;&lt;  xunit -Version 2.1.0
    + CategoryInfo          : NotSpecified: (:) [Install-Package], Exception
    + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PackageManagement.PowerShellCmdlets.InstallPackageCommand</p>

<p>Any ideas on whats going wrong? Sadly google is not giving me anything helpful..</p>
