fix(buttons|modals): prevent modal footer item overflow

[jzempel]

• BREAKING CHANGE?

Description

• Update .c-btn to use text-overflow: ellipsis.
• Update .c-dialog__footer__item display flex with min-width: 0.

Detail

Demo published for review https://garden.zendesk.com/css-components/modals/ (use Playground to test).

Before

After

Checklist

• 👌 style updates are Garden Designer approved (add the
  designer as a reviewer)
• 🌐 component demo is up-to-date (yarn start)
• ✅ all component states are represented
  (.is-hovered, .is-focused, etc.)
• ⬅️ renders as expected with reversed (RTL) direction
• 🤘 renders as expected sans Bedrock (?bedrock=false)
• 📝 tested in Chrome, Firefox, Safari, Edge, and IE11

[yara-simargil]

Wow, thank you for the fix! 🎉