Upgrade stylelint to 12.0.0

[ybiquitous]

Fix #45

See https://github.com/stylelint/stylelint/releases/tag/12.0.0

[YozhikM]

LGTM

[ybiquitous]

yarn install is run on Travis CI, but the current yarn.lock is outdated. See below.

stylelint-a11y/yarn.lock

Lines 5645 to 5646 in 1c522f6

	stylelint@^10.0.1:
	version "10.0.1"

I think better to remove yarn.lock and package-lock.json.

[ybiquitous]

@YozhikM Thank you for your review and quick merge! What do you think about #46 (comment)?

[ybiquitous]

Another option:

• To remove package-lock.json and keep yarn.lock up-to-date.

[YozhikM]

We can try to remove package-lock.json and leave yarn.lock. Of course you need to update it

[ybiquitous]

Thanks. If you feel hard to keep yarn.lock up-to-date, I recommend any lockfiles and open #47 as PoC.