Delegation unvote button showing in black text instead of white

[sauloperez]

Description

The delegation vote button broke its styling with the upgrade to Decidim 0.22 and it is not consistent with Dedicim's regular unvote button. See below.

Proposed solution

This has to do with:

https://github.com/coopdevs/decidim-module-action_delegator/blob/ab8fad14677529202808e878d58364faf4479ab8/app/assets/stylesheets/decidim/action_delegator/questions.scss#L21-L24

It should set the font color to white as Decidim's .question-vote-cabin .vote-button-caption does.