[ColourRole] fix unexpected error due to cooldown

[slushiegoose]

Summary

closes #216 by fixing the unexpected error due to cooldown

Checklist

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)

• Have you tested the changes? (pytest & dpytest)
• Have you followed PEP-8 for naming and styling?
• Has your code been properly documented with RestructuredText docstrings?
• Have you added your changes to CHANGELOG.md under the [Unreleased] heading?
• If your code added new bot commands, have you updated documentation.json?

• All of this code is your own, or follows the author repo's licence.

[codecov]

Codecov Report

Merging #228 (f7d3a31) into master (b4f0b87) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #228      +/-   ##
==========================================
- Coverage   83.48%   83.46%   -0.02%     
==========================================
  Files          27       27              
  Lines        6671     6672       +1     
==========================================
  Hits         5569     5569              
- Misses       1102     1103       +1     

Flag	Coverage Δ
unittests	83.46% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cogs/ColourRole.py	88.55% <0.00%> (-0.30%)	⬇️

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[Kaspiaan]

Please also add changes made to the changelog, you can pretty much put the issue name under a Colour Role heading

[Kaspiaan]

It may seem trivial, but please add this onto the changelog so we have an idea of what's been changed as we go along.

Edit: Apologies for the double comment, forgot I'd already done a comment of this exact thing.

[VirajShah18]

CodeCoverage Fails after 1s - Need to take a look at.