fix(migrate):修正数据库迁移脚本中的错误。

migration/20220921143001_maintenance.up.sql

@@ -7,7 +7,7 @@ alter table end_user_detail
     drop column public_consumption_diluted;
 
 alter table maintenance_fee
-    add column period varchar(10) not null;
+    add column period varchar(10);
 
 alter table report_summary
     drop column customer_consumption,