Change io_service to io_context

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

Change-Id: Ib56544a0a7478990d18fe9e0bbbd8db1e52fa5b8
Signed-off-by: Ed Tanous <edtanous@google.com>
diff --git a/src/Thresholds.hpp b/src/Thresholds.hpp
index cd89efc..a89c1dc 100644
--- a/src/Thresholds.hpp
+++ b/src/Thresholds.hpp
@@ -2,7 +2,7 @@
 
 #include "Utils.hpp"
 
-#include <boost/asio/io_service.hpp>
+#include <boost/asio/io_context.hpp>
 #include <boost/asio/steady_timer.hpp>
 #include <nlohmann/json.hpp>
 
@@ -69,7 +69,7 @@
 struct ThresholdTimer
 {
 
-    explicit ThresholdTimer(boost::asio::io_service& ioService) : io(ioService)
+    explicit ThresholdTimer(boost::asio::io_context& ioService) : io(ioService)
     {}
 
     bool hasActiveTimer(const Threshold& threshold, bool assert)
@@ -111,7 +111,7 @@
                     const Threshold& threshold, bool assert,
                     double assertValue);
 
-    boost::asio::io_service& io;
+    boost::asio::io_context& io;
     std::list<TimerPair> timers;
 };