Add missing template parameters to register_map and register_vector

[tikoyes94]

Add missing template args to register_map and register_vector to allow this kind of bindings:

#include <emscripten.h>
#include <emscripten/bind.h>

std::map<std::string, std::string, std::greater<std::string>> get_map() {
  std::map<std::string, std::string, std::greater<std::string>> m;
  m["a"] = "b";
  m["c"] = "d";
  return m;
}

EMSCRIPTEN_BINDINGS(test_map) {
  emscripten::register_map<std::string, std::string, std::greater<std::string>>("StringMap");
  emscripten::function("get_map", &get_map);
}