build(package): fix relative path of project reference

update the project reference path to use correct relative path

Author: sunquakes

DevTools.Package/DevTools.Package.wapproj

@@ -52,7 +52,7 @@
     </AppxManifest>
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="DevTools.csproj">
+    <ProjectReference Include="..\DevTools.csproj">
       <SkipGetTargetFrameworkProperties>true</SkipGetTargetFrameworkProperties>
     </ProjectReference>
   </ItemGroup>