Red Tests were fixed

Unused 'using' directive were removed.

Octokit.Tests/Reactive/ObservableRepositoryDeployKeysClientTests.cs

@@ -1,10 +1,6 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 using NSubstitute;
-using NSubstitute.Core;
 using Octokit.Reactive;
 using Xunit;
 
@@ -12,7 +8,7 @@ namespace Octokit.Tests.Reactive
 {
     public class ObservableRepositoryDeployKeysClientTests
     {
-        public class TheConstructor
+        public class TheCtor
         {
             [Fact]
             public void ThrowsForBadArgs()