[doc] %s/itirate/iterate/g

[zhjwpku]

Signed-off-by: Junwang Zhao [email protected]

Here are some reminders before you submit the pull request

• [ ] Add tests for the change
• [ ] Document changes
• [ ] Communicate in the mailing list if needed
• [ ] Pass make installcheck
• [ ] Review a PR in return to support the community