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/RepositoryCommitsClientTests.cs

@@ -92,7 +92,7 @@ public class RepositoryCommitsClientTests
 
             var repoName = Helper.MakeNameWithTimestamp("source-repo");
 
-            _repository = _client.Repository.Create(new NewRepository { Name = repoName, AutoInit = true }).Result;
+            _repository = _client.Repository.Create(new NewRepository(repoName) { AutoInit = true }).Result;
         }
 
         [IntegrationTest]