modify json.hpp to compile with recent gcc

ext/json.hpp

@@ -6379,10 +6379,12 @@ class basic_json
         {
             switch (lhs_type)
             {
-//                case value_t::array:
+                case value_t::array:
-//                {
+                {
                     //return *lhs.m_value.array < *rhs.m_value.array;
-//                }
+                    return *lhs.m_value.array.operator<(lhs, rhs);
+                   // return nlohmann::detail::operator<(lhs, rhs);
+                }
                 case value_t::object:
                 {
                     return *lhs.m_value.object < *rhs.m_value.object;