Fixed strong name signing.

Directory.Build.props

@@ -19,11 +19,6 @@
     <PackageOutputPath>$(MSBuildThisFileDirectory)bin\nupkg</PackageOutputPath>
   </PropertyGroup>
 
-  <PropertyGroup>
-    <SignAssembly Condition="'$(SignAssembly)' == '' and '$(IsUwpProject)' != 'true' and '$(IsTestSampleProject)' != 'true'" >true</SignAssembly>
-    <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)toolkit.snk</AssemblyOriginatorKeyFile>
-  </PropertyGroup>
-
   <PropertyGroup Condition="'$(TF_BUILD)' == 'true'">
     <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
   </PropertyGroup>

Directory.Build.targets

@@ -21,6 +21,15 @@
       </ItemGroup>
     </When>
   </Choose>
+  
+  <Choose>
+    <When Condition="$(TargetFramework.Contains('uap10.0')) == false and '$(TargetFramework)' != 'native' and '$(IsTestSampleProject)' != 'true'">
+      <PropertyGroup>
+        <SignAssembly>true</SignAssembly>
+        <AssemblyOriginatorKeyFile>$(MSBuildThisFileDirectory)toolkit.snk</AssemblyOriginatorKeyFile>
+      </PropertyGroup>
+    </When>
+  </Choose>
 
   <Target Name="AddCommitHashToAssemblyAttributes" BeforeTargets="GetAssemblyAttributes">
     <ItemGroup>