Fix instance builder tests - missing fsharp using

Author: hadzhiyski

tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs

@@ -4,16 +4,15 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
-
+using Microsoft.FSharp.Core;
 using CommandLine.Core;
 using CommandLine.Infrastructure;
-using CommandLine.Tests.Fakes;
 
 using CSharpx;
-
+using CommandLine.Tests.Fakes;
 using FluentAssertions;
-
 using Xunit;
+using System.Reflection;
 
 namespace CommandLine.Tests.Unit.Core
 {