bmcweb: move variant usage to std namespace

Change-Id: I9d7069668f91f2ac72d2f4a440f63e0e85dd5269
Signed-off-by: Ed Tanous <ed.tanous@intel.com>
diff --git a/include/dbus_monitor.hpp b/include/dbus_monitor.hpp
index d4f2647..1b82697 100644
--- a/include/dbus_monitor.hpp
+++ b/include/dbus_monitor.hpp
@@ -8,15 +8,15 @@
 #include <openbmc_dbus_rest.hpp>
 #include <sdbusplus/bus/match.hpp>
 #include <sdbusplus/message/types.hpp>
+#include <variant>
 
 namespace nlohmann
 {
-template <typename... Args>
-struct adl_serializer<sdbusplus::message::variant<Args...>>
+template <typename... Args> struct adl_serializer<std::variant<Args...>>
 {
-    static void to_json(json& j, const sdbusplus::message::variant<Args...>& v)
+    static void to_json(json& j, const std::variant<Args...>& v)
     {
-        sdbusplus::message::variant_ns::visit([&](auto&& val) { j = val; }, v);
+        std::visit([&](auto&& val) { j = val; }, v);
     }
 };
 } // namespace nlohmann