Upgrade postcss-values-parser dep to v3 to remove deprecated package message

[marcofugaro]

Currently when using this plugin, this appears in the console.

postcss-color-mod-function > postcss-values-parser > flatten@1.0.2: I wrote this module a very long time ago; you should use something else.

This was already solved in shellscape/postcss-values-parser#86, upgrading the dependency would solve the issue.

[feimosi]

Agreed, same here, would be great to have this package upgraded.

[Twissi]

yes, postcss-values-parser should be bumped to version 3.0.5.
I can easily do that, but how can I make sure the update doesn't breaks anything?

[carlosjeurissen]

This would indeed be very welcome. @Twissi seems this package already has tests.