Method ordered_map

lesson6-Segmentation/json.hpp:16417–16417

Explicit constructors instead of `using Container::Container` otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)

    // Explicit constructors instead of `using Container::Container`
    // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
    ordered_map(const Allocator& alloc = Allocator()) : Container{alloc} {}
    template <class It>
    ordered_map(It first, It last, const Allocator& alloc = Allocator())
        : Container{first, last, alloc} {}