Update helix.proj

Author: HaoK

eng/helix/helix.proj

@@ -1,5 +1,6 @@
 <Project Sdk="Microsoft.DotNet.Helix.Sdk" DefaultTargets="Test" TreatAsLocalProperty="ProjectToBuild">
-
+  <Import Project="Sdk.props" Sdk="Microsoft.NET.Sdk" />
+  
   <PropertyGroup>
     <!--
       When invoking helix.proj for the whole repo with build.cmd, ProjectToBuild will be set to the path to this project.