fix io_service incomplete type compile errors

refs #4425

Change-Id: I8969593ae00fb78d4ae9e686b133bca134accb22
diff --git a/tools/ndnrepowatch.cpp b/tools/ndnrepowatch.cpp
index 16be915..0707c87 100644
--- a/tools/ndnrepowatch.cpp
+++ b/tools/ndnrepowatch.cpp
@@ -33,6 +33,7 @@
 #include <iostream>
 #include <string>
 
+#include <boost/asio/io_service.hpp>
 #include <boost/lexical_cast.hpp>
 
 namespace repo {