Restore colors parameter of donut chart partial

[AndrewKvalheim]

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the upstream master branch.
• The tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works (if appropriate).
• I have added necessary documentation (if appropriate).

Short description of what this resolves

Some donut charts are all black:

• Administration → Events
• Administration → Users
• Manage conference → Events → Events state

Changes proposed in this pull request

Pass the colors parameter of the donut chart partial to Chartkick.