index.js
function (permissions) {
    _.merge(this.permissions, permissions, function (a, b) {
      return _.isArray(a) ? a.concat(b) : undefined;
    });
    return this;
  }
function (permissions) {
    _.merge(this.permissions, permissions, function (a, b) {
      return _.isArray(a) ? a.concat(b) : undefined;
    });
    return this;
  }
allows additional permissions for this acl

@param  {Object} permissions