title: The attribute "Version" in element <PackageReference> is unrecognized
body: <p>I have a solution with many projects that target .net 4.6.1. On our MS build server it builds just fine. I recently added a project that targets .NET Standard 1.3. This will not build on the build server. It builds locally with VS2017 just fine. Build server VS has just been updated with all the latest. </p>
  
  <p>The build error I'm getting is: <code>The attribute "Version" in element &lt;PackageReference&gt; is unrecognized.</code></p>
  
  <p>I am getting this for a few references. Here's one pulled from the project file: <code>&lt;PackageReference Include="System.Diagnostics.Process" Version="4.3.0"/&gt;</code></p>
  
  <p>Any ideas?</p>