Have countdowns in the Timelist use a - symbol

[scottbell]

Closes #7450

Describe your changes:

Pretty simple fix to add a - for countdown Timelist entries.

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• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Is this change backwards compatible? For example, developers won't need to change how they are calling the API or how they've extended core plugins such as Tables or Plots.

Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
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Reviewer Checklist

• Changes appear to address issue?
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (18e4b9d) 55.59% compared to head (135e714) 55.64%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7452      +/-   ##
==========================================
+ Coverage   55.59%   55.64%   +0.05%     
==========================================
  Files         668      668              
  Lines       26800    26800              
  Branches     2606     2606              
==========================================
+ Hits        14899    14913      +14     
+ Misses      11186    11171      -15     
- Partials      715      716       +1     

Flag	Coverage Δ
e2e-full	49.01% <ø> (-0.01%)	⬇️
e2e-stable	59.35% <ø> (+0.24%)	⬆️
unit	48.59% <ø> (-0.01%)	⬇️

Files	Coverage Δ
src/plugins/timelist/TimelistComponent.vue	56.81% <ø> (ø)

... and 6 files with indirect coverage changes

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[ozyx]

LGTM. Nice!