mysql CURRENT_TIMESTAMP not support

I use this def:

```sh
Table group_log {
id int [pk, not null, increment]
add_time timestamp [not null, default: `CURRENT_TIMESTAMP`]
}
```

create this SQL for mysql:
```sql
CREATE TABLE `group_log` (
`id` bigint PRIMARY KEY NOT NULL AUTO_INCREMENT,
`add_time` timestamp NOT NULL DEFAULT (CURRENT_TIMESTAMP),
);
```

get this error:
```sh
#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '(CURRENT_TIMESTAMP),
)' at line 3
```

try with this:
```sh
default: `CURRENT_TIMESTAMP`
```

generate this: ` add_time timestamp NOT NULL DEFAULT (CURRENT_TIMESTAMP())`, also not work for MYSQL