Fix missing header <optional>

Signed-off-by: Tom Joseph <rushtotom@gmail.com>
Change-Id: If444bb6e93413e97bfb11c0755d90f1b5bcbb42e
diff --git a/libpldmresponder/fru_parser.hpp b/libpldmresponder/fru_parser.hpp
index aec27cb..ce09986 100644
--- a/libpldmresponder/fru_parser.hpp
+++ b/libpldmresponder/fru_parser.hpp
@@ -2,6 +2,7 @@
 
 #include <filesystem>
 #include <map>
+#include <optional>
 #include <set>
 #include <string>
 #include <tuple>