Merge pull request microsoft#248 from microsoft/dev/willxie/sign

Fix signing XdtExtensions.dll

Author: willxie-eng

src/InstrumentationEngine.XdtExtensions/XdtExtensions.csproj

@@ -11,6 +11,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.Web.Xdt" Version="1.4.0" />
+    <PackageReference Include="Microsoft.VisualStudioEng.MicroBuild.Core" Version="$(MicroBuildCoreVersion)" />
   </ItemGroup>
   <Import Project="Sdk.targets" Sdk="Microsoft.NET.Sdk" />
   <Import Project="$(EnlistmentRoot)\build\Common.targets" />