fix test build

Author: moh-hassan

tests/CommandLine.Tests/Unit/Text/HelpTextTests.cs

@@ -2,6 +2,8 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
+using CommandLine.Core;
 using System.Linq;
 using System.Reflection;
 using CommandLine.Infrastructure;