added missing properties to IObservableIssuesClient

Octokit.Reactive/Clients/ObservableIssuesLabelsClient.cs

@@ -0,0 +1,15 @@
+namespace Octokit.Reactive
+{
+    public class ObservableIssuesLabelsClient : IObservableIssuesLabelsClient
+    {
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1823:AvoidUnusedPrivateFields")]
+        IIssuesLabelsClient _client;
+
+        public ObservableIssuesLabelsClient(IGitHubClient client)
+        {
+            Ensure.ArgumentNotNull(client, "client");
+
+            _client = client.Issue.Labels;
+        }
+    }
+}