Fix tests with DataFrames 0.22 on Julia 1.5

[nalimilan]

No description provided.

[rikhuijzer]

Note that if you run the CI after upgrading CategoricalArrays so that DataFrames goes to 0.22, one test will fail (https://github.com/GiovineItalia/Gadfly.jl/runs/1417459612).

@nalimilan can you trigger CI again?

[codecov-io]

Codecov Report

Merging #1499 (10050de) into master (3a6da5a) will increase coverage by 0.77%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1499      +/-   ##
==========================================
+ Coverage   88.94%   89.71%   +0.77%     
==========================================
  Files          39       39              
  Lines        4395     4601     +206     
==========================================
+ Hits         3909     4128     +219     
+ Misses        486      473      -13     

Impacted Files	Coverage Δ
src/ticks.jl	91.09% <0.00%> (-0.28%)	⬇️
src/shapes.jl	100.00% <0.00%> (ø)
src/geom/line.jl	100.00% <0.00%> (ø)
src/geom/point.jl	100.00% <0.00%> (ø)
src/geom/ribbon.jl	100.00% <0.00%> (ø)
src/geom/violin.jl	100.00% <0.00%> (ø)
src/geom/boxplot.jl	100.00% <0.00%> (ø)
src/geom/polygon.jl	100.00% <0.00%> (ø)
src/dataframes.jl	97.61% <0.00%> (+0.05%)	⬆️
src/geom/label.jl	96.33% <0.00%> (+0.06%)	⬆️
... and 24 more

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[nalimilan]

Thanks. I've added a fix for that test. But CI still uses DataFrames 0.21.8 (not sure why since I've just updated RDatasets to allow 0.22, and CSV doesn't depend on DataFrames).

EDIT: Got it, that because we need #1496 to support RDatasets 0.7 first. I don't know why I can't find a mention of that conflict now in the logs. Where are the missing lines showing the packages used during testing?

[rikhuijzer]

That other PR is mostly working on fixing the failing Julia 1.0 (LTS). What happens if you bump RDatasets? (Note that I can't do it for you because I'm not an official maintainer here at Gadfly. I just saw something at my PR which might help your PR out.)

[nalimilan]

Tests now pass with DataFrames 0.22 on Julia 1.5.