function defaults(options, _defaults) {
  options = options || {};
  eachKey(_defaults, function(key, val) {
    if (!existy(options[key])) {
      options[key] = val;
    }
  });
  return options;
}
Set default options where some option was not specified.

@param {Object} options The destination
@param {Object} _defaults The defaults
@returns {Object}