Change io_service to io_context

This was renamed a while back in boost to be compliant with the
std::executors proposal.

Change-Id: Ie95657cdff79b725d189ee0b36de72813248b52e
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/src/main.cpp b/src/main.cpp
index f104f22..d04ea99 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -325,7 +325,7 @@
 
 int main()
 {
-    boost::asio::io_service io;
+    boost::asio::io_context io;
     auto conn = std::make_shared<sdbusplus::asio::connection>(io);
     timer = std::make_unique<boost::asio::steady_timer>(io);
     initTimer = std::make_unique<boost::asio::steady_timer>(io);