有些PHP版本要求设置date.timezone, 否则报错。

It is not safe to rely on the system's timezone settings.
You are *required* to use the date.timezone setting or the date_default_timezone_set() function.
In case you used any of those methods and you are still getting this warning,
you most likely misspelled the timezone identifier.

1. 在php.ini中，设置date.timezone的默认值。
2. 重启apache即可。