CompatHelper: bump compat for "RecipesBase" to "0.8"

[github-actions]

This pull request changes the compat entry for the RecipesBase package from 0.6.0, 0.7 to 0.6.0, 0.7, 0.8.

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 #67 into master will increase coverage by 0.73%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
+ Coverage   96.34%   97.07%   +0.73%     
==========================================
  Files          12       12              
  Lines         547      547              
==========================================
+ Hits          527      531       +4     
+ Misses         20       16       -4

Impacted Files	Coverage Δ
src/derivatives-type.jl	100% <0%> (ø)	⬆️
src/math.jl	99.65% <0%> (ø)	⬆️
src/show.jl	72.72% <0%> (+6.06%)	⬆️
src/conversions.jl	87.5% <0%> (+6.25%)	⬆️
src/comparisons-tests.jl	86.66% <0%> (+6.66%)	⬆️

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