Merge pull request #219 from github/update-octokit-0.18

Bump octokit.net to v0.18

Author: shana

src/UnitTests/GitHub.App/Models/ModelServiceTests.cs

@@ -615,7 +615,8 @@ static PullRequest CreatePullRequest(User user, int id, ItemState state, string
         var uri = new Uri("https://url");
         return new PullRequest(uri, uri, uri, uri, uri, uri,
             id, state, title, "", createdAt, updatedAt,
-            null, null, null, null, user, "", false, null, null, commentCount, 0, 0, 0,
-            0);
+            null, null, null, null, user, null, false, null,
+            commentCount, 0, 0, 0, 0,
+            null, false);
     }
 }