Remove reference to old Cobalt colours in docs

[Athenodoros]

I haven't filed an issue, but I think this is a pretty simple change.

Checklist

• Includes tests
• Update documentation

Changes proposed in this pull request:

The qualitative colour array used to reference the Cobalt3, but is rendering empty now that it's been removed. This replaces it with cerulean, which seems like the closest option now.

[changelog-app]

Generate changelog in packages/docs-app/changelog/@unreleased

What do the change types mean?

• feature: A new feature of the service.
• improvement: An incremental improvement in the functionality or operation of the service.
• fix: Remedies the incorrect behaviour of a component of the service in a backwards-compatible way.
• break: Has the potential to break consumers of this service's API, inclusive of both Palantir services
  and external consumers of the service's API (e.g. customer-written software or integrations).
• deprecation: Advertises the intention to remove service functionality without any change to the
  operation of the service itself.
• manualTask: Requires the possibility of manual intervention (running a script, eyeballing configuration,
  performing database surgery, ...) at the time of upgrade for it to succeed.
• migration: A fully automatic upgrade migration task with no engineer input required.

Note: only one type should be chosen.

How are new versions calculated?

• ❗The break and manual task changelog types will result in a major release!
• 🐛 The fix changelog type will result in a minor release in most cases, and a patch release version for patch branches. This behaviour is configurable in autorelease.
• ✨ All others will result in a minor version release.

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Remove reference to old Cobalt colours in docs

Check the box to generate changelog(s)

• Generate changelog entry

[svc-palantir-github]

Add generated changelog entries

Build artifact links for this commit: documentation | landing | table | demo

This is an automated comment from the deploy-preview CircleCI job.

[ggdouglas]

Thanks for the fix!