Update C++ server with new core API

And reflects the C++ API in ServerBuilder.
diff --git a/examples/pubsub/subscriber_test.cc b/examples/pubsub/subscriber_test.cc
index 1fdcc8f..49738fc 100644
--- a/examples/pubsub/subscriber_test.cc
+++ b/examples/pubsub/subscriber_test.cc
@@ -40,6 +40,7 @@
 #include <grpc++/server.h>
 #include <grpc++/server_builder.h>
 #include <grpc++/server_context.h>
+#include <grpc++/server_credentials.h>
 #include <grpc++/status.h>
 #include <gtest/gtest.h>
 
@@ -105,11 +106,11 @@
     int port = grpc_pick_unused_port_or_die();
     server_address_ << "localhost:" << port;
     ServerBuilder builder;
-    builder.AddPort(server_address_.str());
+    builder.AddPort(server_address_.str(), grpc::InsecureServerCredentials());
     builder.RegisterService(&service_);
     server_ = builder.BuildAndStart();
 
-    channel_ = CreateChannel(server_address_.str(), ChannelArguments());
+    channel_ = CreateChannel(server_address_.str(), grpc::InsecureCredentials(), ChannelArguments());
 
     subscriber_.reset(new grpc::examples::pubsub::Subscriber(channel_));
   }