Merge pull request #3345 from murgatroid99/node_callback_this

Fixed a couple of incorrect "this" references in Node library
diff --git a/src/csharp/Grpc.IntegrationTesting/InteropClient.cs b/src/csharp/Grpc.IntegrationTesting/InteropClient.cs
index 0884c6e..616093d 100644
--- a/src/csharp/Grpc.IntegrationTesting/InteropClient.cs
+++ b/src/csharp/Grpc.IntegrationTesting/InteropClient.cs
@@ -131,7 +131,7 @@
             var channel = new Channel(options.ServerHost, options.ServerPort, credentials, channelOptions);
             TestService.TestServiceClient client = new TestService.TestServiceClient(channel);
             await RunTestCaseAsync(client, options);
-            channel.ShutdownAsync().Wait();
+            await channel.ShutdownAsync();
         }
 
         private async Task RunTestCaseAsync(TestService.TestServiceClient client, ClientOptions options)