Ignore commented lines when using update prefix

[SanjulaGanepola]

Fixes #386

Testable using:

update: select * from sample.employee
--  where job = 'MANAGER'
order by empno;

[forstie]

Could I please get a vsix for this one?

[SanjulaGanepola]

@forstie Since this is from a fork, it didn't trigger a build of the VSIX. It's also blocking me from uploading one here so I'll send it over on our Slack thread.

Liam got us write access so the next PRs will have them.

[forstie]

reviewed and tested, works great