Error Array to string conversion for Yii::$app->user->id

解决方法如下：

1. ALTER TABLE `user` ADD PRIMARY KEY(`id`);
2. i remove manually from the browser the cookie and it work.

参考：

https://stackoverflow.com/questions/44499961/error-array-to-string-conversion-for-yiiapp-user-id

https://github.com/yiisoft/yii2/issues/1029

https://stackoverflow.com/questions/27681505/login-on-production-server-doesnt-work