npm start 启动报错
npm start 启动报错，报错信息是不能加入有约束的外键
```
koa deprecated Support for generators will be removed in v3. See the documentation for examples of how to convert old middleware https://github.com/koajs/koa/blob/master/docs/migration.md app.js:18:5
Executing (default): CREATE TABLE IF NOT EXISTS `user` (`id` INTEGER(11) NOT NULL auto_increment , `username` VARCHAR(50) NOT NULL, `password` VARCHAR(255) NOT NULL, `createdAt` DATETIME, `updatedAt` DATETIME, PRIMARY KEY (`id`)) ENGINE=InnoDB;
Executing (default): CREATE TABLE IF NOT EXISTS `article` (`id` INTEGER auto_increment , `title` VARCHAR(255) NOT NULL, `author` VARCHAR(255) NOT NULL, `recommend` TINYINT(1) NOT NULL DEFAULT false, `introduce` VARCHAR(255) NOT NULL, `category` VARCHAR(255) NOT NULL, `banner` VARCHAR(255) NOT NULL, `content` TEXT NOT NULL, `browser` INTEGER DEFAULT 0, `createdAt` DATETIME, `updatedAt` DATETIME, `categoryId` INTEGER, PRIMARY KEY (`id`), FOREIGN KEY (`categoryId`) REFERENCES `category` (`id`) ON DELETE SET NULL ON UPDATE CASCADE) ENGINE=InnoDB;
Executing (default): CREATE TABLE IF NOT EXISTS `category` (`id` INTEGER auto_increment , `name` VARCHAR(50) NOT NULL, `createdAt` DATETIME, `updatedAt` DATETIME, PRIMARY KEY (`id`)) ENGINE=InnoDB;
Unhandled rejection SequelizeDatabaseError: Cannot add foreign key constraint
    at Query.formatError (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/sequelize/lib/dialects/mysql/query.js:247:16)
    at Query.handler [as onResult] (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/sequelize/lib/dialects/mysql/query.js:68:23)
    at Query.Command.execute (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/mysql2/lib/commands/command.js:30:12)
    at Connection.handlePacket (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/mysql2/lib/connection.js:502:28)
    at PacketParser.onPacket (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/mysql2/lib/connection.js:81:16)
    at PacketParser.executeStart (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/mysql2/lib/packet_parser.js:77:14)
    at Socket.<anonymous> (/Users/Leo/my/projects/test/nodejs-koa2-mysql-sequelize-jwt/node_modules/mysql2/lib/connection.js:89:29)
    at emitOne (events.js:116:13)
    at Socket.emit (events.js:211:7)
    at addChunk (_stream_readable.js:263:12)
    at readableAddChunk (_stream_readable.js:250:11)
    at Socket.Readable.push (_stream_readable.js:208:10)
    at TCP.onread (net.js:597:20)

Executing (default): SHOW INDEX FROM `user`
Executing (default): SHOW INDEX FROM `category`
```