tools: switch to Face::getIoContext()

Change-Id: I550dc4dd9dc6509b7df3104b8cd68865653df541
diff --git a/tools/ndncert-ca-server.cpp b/tools/ndncert-ca-server.cpp
index 566f355..a683a9f 100644
--- a/tools/ndncert-ca-server.cpp
+++ b/tools/ndncert-ca-server.cpp
@@ -72,14 +72,14 @@
     std::cerr << signalName;
   }
   std::cerr << std::endl;
-  face.getIoService().stop();
+  face.getIoContext().stop();
   exit(1);
 }
 
 static int
 main(int argc, char* argv[])
 {
-  boost::asio::signal_set terminateSignals(face.getIoService());
+  boost::asio::signal_set terminateSignals(face.getIoContext());
   terminateSignals.add(SIGINT);
   terminateSignals.add(SIGTERM);
   terminateSignals.async_wait(handleSignal);