Prefer `asio::io_context` over `asio::io_service`

Change-Id: I08f136b49e0f03e30d26803be030497ec22eb01f
diff --git a/src/repo.hpp b/src/repo.hpp
index 9b7630e..68f339f 100644
--- a/src/repo.hpp
+++ b/src/repo.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2022, Regents of the University of California.
+ * Copyright (c) 2014-2023, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -66,9 +66,9 @@
   };
 
 public:
-  Repo(boost::asio::io_service& ioService, const RepoConfig& config);
+  Repo(boost::asio::io_context& io, const RepoConfig& config);
 
-  //@brief rebuild index from storage file when repo starts.
+  /// @brief Rebuild index from storage file when repo starts.
   void
   initializeStorage();