Update dependencies from https://github.com/dotnet/arcade build 20190311.14

This change updates the following dependencies
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19161.14

eng/common/generate-graph-files.ps1

@@ -42,7 +42,7 @@ try {
   }
 
   Write-Host "Generating dependency graph..."
-  $darc = Invoke-Expression "& `"$darcExe`" $options"
+  Invoke-Expression "& `"$darcExe`" $options"
   CheckExitCode "Generating dependency graph"
   
   $graph = Get-Content $graphVizFilePath