Use PostCSS 8 events

[ai]

Using the Once event is not a good practice. postcss-custom-media will not see changes made by other plugins (for instance, by postcss-mixins).

Moving to the AtRule event will improve other plugins' support.

[alexgagnon]

I put in a PR for this here: #66

[dmgawel]

@jonathantneal looks like #66 is already merged. Would it be possible to mark a new release containing that change to resolve this issue?

[blvdmitry]

After updating to postcss 8, postcss-custom-media stopped working together with postcss-each and I assume it could be related to this issue.
@jonathantneal Since a solution for it has been already merged – is there a chance we can have a patch release with it?

[sevilyilmaz]

@ai would it be possible to have the fix released by another member of PostCSS instead of being blocked by one?

[ai]

@sevilyilmaz I can try to release if we have PR

[IgorLesnevskiy]

@ai as far as I can see, the fix was merged a long time ago. I created a merge request - #76. I'm not familiar with the postcss release flow, but I guess you can merge it, create a tag and publish the package?

[spacedawwwg]

Is the package getting a bump?