This will add the non-default nuget key to avoid compilation error. (#390)

* This will add the non-default nuget key to avoid compilation error.

* addressing comment

Author: thaystg

NuGet.config

@@ -1,5 +1,6 @@
 <configuration>
     <config>
         <add key="repositoryPath" value="packages" />
+        <add key="dotnet-tools" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json" />
     </config>
 </configuration>