CompatHelper: bump compat for "Colors" to "0.12"

[github-actions]

This pull request changes the compat entry for the Colors package from 0.9, 0.10, 0.11 to 0.9, 0.10, 0.11, 0.12.

This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry. It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov-io]

Codecov Report

Merging #1401 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1401      +/-   ##
==========================================
+ Coverage   90.31%   90.36%   +0.05%     
==========================================
  Files          39       39              
  Lines        4242     4060     -182     
==========================================
- Hits         3831     3669     -162     
+ Misses        411      391      -20     

Impacted Files	Coverage Δ
src/color_misc.jl	62.06% <0.00%> (-2.45%)	⬇️
src/misc.jl	65.77% <0.00%> (-1.75%)	⬇️
src/ticks.jl	90.32% <0.00%> (-1.05%)	⬇️
src/bincount.jl	95.34% <0.00%> (-0.53%)	⬇️
src/Gadfly.jl	78.64% <0.00%> (-0.48%)	⬇️
src/mapping.jl	84.46% <0.00%> (-0.44%)	⬇️
src/coord.jl	91.57% <0.00%> (-0.35%)	⬇️
src/geom/subplot.jl	95.30% <0.00%> (-0.24%)	⬇️
src/geom/segment.jl	94.44% <0.00%> (-0.16%)	⬇️
src/dataframes.jl	97.43% <0.00%> (-0.13%)	⬇️
... and 13 more

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