why after I adding ' -assume-rbr' it still bothers with 'Needed: SUPER|' ?

> This is the place to report a bug, ask a question, or suggest an enhancement.
Hi, I use latest version gh-ost, I need change table colume length, not sure why it bothered.

connect to azure mysql
add '-assume-rbr ' already

full cmd:
```
./gh-ost -azure -exact-rowcount --concurrent-rowcount -user "user@mysql" -password "password" \
-host "mysql.mysql.database.chinacloudapi.cn" -port 3306 \
-allow-on-master -database "xiaoshu" --verbose -table "customer" \
-alter " change campaign_id campaign_id varchar(64)" \
-assume-rbr --master-user="user@mysql" --master-password="passwd" --assume-master-host=mysql.mysql.database.chinacloudapi.cn --execute
```

it told me error like:
```
SUPER|REPLICATION CLIENT, REPLICATION SLAVE and ALL on `dbname`.*
```
> This is also the place to make a discussion before creating a PR.

> If this is a bug report, please provide a test case (e.g., your table definition and gh-ost command) and the error output.

> Please use markdown to format code or SQL: https://guides.github.com/features/mastering-markdown/

> Please label the issue on the right (bug, enhancement, question, etc.).
```
2021-08-23 04:10:20 FATAL 2021-08-23 04:10:20 ERROR User has insufficient privileges for migration. Needed: SUPER|REPLICATION CLIENT, REPLICATION SLAVE and ALL on `dbname`.*
```
> And please understand if this issue is not addressed immediately or in a timeframe you were expecting.

> Thank you!