text: exports.up = function(db, callback) {
      db.runSql(
          `ALTER TABLE ${db.schema}.features ADD "last_seen_at" datetime default current_timestamp`,
          callback,
      );
  };
  
  exports.down = function(db, cb) {
      return db.removeColumn(`${db.schema}.features`, 'last_seen_at', cb);
  };
  