tests: Add missing asio::system_executor include.

Closes #41

Author: biljazovic

test/unit/logger.cpp

@@ -14,6 +14,7 @@
 #include <boost/asio/detached.hpp>
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/system_executor.hpp>
 #include <boost/system/error_code.hpp>
 #include <boost/test/tools/output_test_stream.hpp>
 #include <boost/test/unit_test.hpp>