Repository name is required when creating a repo

I was trying to create a repository and I wasn't sure which parameters
were required. Following our philosophy of exposing required parameters
in the constructor, I change the `NewRepository` object to take in a
repository name and to make that property readonly.

Octokit.Tests.Integration/Clients/MergingClientTests.cs

@@ -23,7 +23,7 @@ public class MergingClientTests : IDisposable
 
         var repoName = Helper.MakeNameWithTimestamp("public-repo");
         _fixture = _client.Repository.Merging;
-        _repository = _client.Repository.Create(new NewRepository { Name = repoName, AutoInit = true }).Result;
+        _repository = _client.Repository.Create(new NewRepository(repoName) { AutoInit = true }).Result;
         _owner = _repository.Owner.Login;
     }