Let DiffServiceTests find Properties.Resources

Required because `GitHub.InlineReviews.Resources` needed to be public.

Author: jcansdale

test/GitHub.InlineReviews.UnitTests/Services/DiffServiceTests.cs

@@ -2,14 +2,15 @@
 using System.IO;
 using System.Linq;
 using GitHub.InlineReviews.Services;
-using GitHub.InlineReviews.UnitTests.Properties;
 using GitHub.Services;
 using GitHub.Models;
 using NSubstitute;
 using Xunit;
 
 namespace GitHub.InlineReviews.UnitTests.Services
 {
+    using Resources = Properties.Resources;
+
     public class DiffServiceTests
     {
         public class TheParseFragmentMethod