Update stylelint peer dependency to include stylelint 15

[alex-e-leon]

Bumps peer dependency to fix: #32

Some quick testing suggests that this plugin works fine with stylelint 15

[alex-e-leon]

For anyone waiting on this, feel free to use my published fork:
@alex-e-leon/stylelint-value-no-unknown-custom-properties": "^4.0.2"

[alex-e-leon]

Hey @Antonio-Laguna - this should be an easy PR to approve - I've been running this branch for the last few weeks and can confidently say that this plugin still works fine with stylelint 15.

Any chance you can get this merged in?

[jameschensmith]

I'm not able to approve (don't have write access), but LGTM 👍

Also, just a note: a very basic implementation of this has been added to stylelint (you can view the details in the initial MR). This tracking issue would probably need to be close for the built-in rule to completely replace this rule.

[alex-e-leon]

Thanks @jameschensmith : )
I know that at least for my usecase, and probably most people who use css-modules, not being able to track definitions in other files would be a dealbreaker.

[Antonio-Laguna]

Thanks @alex-e-leon ! Apologies this took me a while!