[cors] Fix compile error with options.

Fix this error:
@brndnmtthws 

    http.hpp: In constructor 'process::http::OK::OK(const Value&, const Option<std::basic_string<char> >&, const Option<hashmap<std::basic_string<char>, std::basic_string<char> > >&)':
    http.hpp:201:34: error: 'const class Option<hashmap<std::basic_string<char>, std::basic_string<char> > >' has no member named 'begin'
    http.hpp:201:55: error: 'const class Option<hashmap<std::basic_string<char>, std::basic_string<char> > >' has no member named 'end'