code: function strict(query) {
    return foldl(function(acc, val, key) {
      if (has.call(allowedKeys, key)) acc[key] = val;
      return acc;
    }, {}, utm(query));
  }
docs: Get strict utm params - from the given `querystring`
  
  @param {String} query
  @return {Object}
  @api private