http: add missing header bootlegged by boost < 1.72
http: add missing header bootlegged by boost < 1.72

httpserver.cpp:74:10: error: no template named 'deque' in namespace 'std'
    std::deque<std::unique_ptr<WorkItem>> queue;
    ~~~~~^


Former-commit-id: 461a7d6f36b396d19c1177ff84633f042be813d3
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin