fix nonexistent version warning for System.Threading.ThreadPool

src/csharp/Grpc.Core/Grpc.Core.csproj

@@ -65,7 +65,7 @@
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard1.5' ">
     <PackageReference Include="System.Runtime.Loader" Version="4.0.0" />
     <PackageReference Include="System.Threading.Thread" Version="4.0.0" />
-    <PackageReference Include="System.Threading.ThreadPool" Version="4.0.0" />
+    <PackageReference Include="System.Threading.ThreadPool" Version="4.0.10" />
   </ItemGroup>
 
   <Import Project="NativeDeps.csproj.include" />