Update expression-syntax.md (#3288)
Update expression-syntax.md (#3288)

* Update expression-syntax.md

* Update expression-syntax.md

delete spaces

* Update expression-syntax.md

* Apply suggestions from code review

Co-authored-by: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>

Co-authored-by: Keke Yi <4b13e11d5beb5669a80650bc9e0535372af5b679@users.noreply.github.com>
pingcap/docs,pingcap/docs,pingcap/docs