update the sql_mode description (#2679)
update the sql_mode description (#2679)

* update the sql_mode des

* Update sql-mode.md

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs-cn,pingcap/docs-cn