Avoid deprecated Boost.Asio interfaces

Change-Id: I00d285893ff61619f49dff8a8a55d0d0e2c309a7
diff --git a/tests/integration/network-monitor.cpp b/tests/integration/network-monitor.cpp
index cf6d8bd..ff4d932 100644
--- a/tests/integration/network-monitor.cpp
+++ b/tests/integration/network-monitor.cpp
@@ -30,7 +30,7 @@
 #include "ndn-cxx/util/string-helper.hpp"
 #include "ndn-cxx/util/time.hpp"
 
-#include <boost/asio/io_service.hpp>
+#include <boost/asio/io_context.hpp>
 #include <iostream>
 
 namespace ndn::tests {
@@ -48,7 +48,7 @@
 
 BOOST_AUTO_TEST_CASE(Signals)
 {
-  boost::asio::io_service io;
+  boost::asio::io_context io;
   NetworkMonitor monitor(io);
 
   std::cout << "capabilities=" << AsHex{monitor.getCapabilities()} << std::endl;