monitor: `optional` no longer experimental

Change-Id: I29e4fa5cfdf5cefe1af548fd5af2a54d08682a11
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/monitor/json_parser.cpp b/monitor/json_parser.cpp
index 9b773c2..227530f 100644
--- a/monitor/json_parser.cpp
+++ b/monitor/json_parser.cpp
@@ -192,7 +192,7 @@
         }
 
         // Handle optional conditions
-        auto cond = std::experimental::optional<Condition>();
+        auto cond = std::optional<Condition>();
         if (fan.contains("condition"))
         {
             if (!fan["condition"].contains("name"))