[docs] Fix plot was showing twice the same data.

[eavilaes]

On API docs, databricks.koalas.DataFrame.plot.bar, an example plot was showing on its first row two bars per element, both of them showing the same data. Changed it to show different data, so it is visually clearer.

[codecov-commenter]

Codecov Report

Merging #2196 (38bafe9) into master (e971d6f) will decrease coverage by 4.51%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2196      +/-   ##
==========================================
- Coverage   95.32%   90.80%   -4.52%     
==========================================
  Files          60       60              
  Lines       13746    13629     -117     
==========================================
- Hits        13103    12376     -727     
- Misses        643     1253     +610     

Impacted Files	Coverage Δ
databricks/koalas/plot/core.py	91.49% <ø> (-2.28%)	:arrow_down:
databricks/koalas/plot/plotly.py	15.15% <0.00%> (-80.81%)	:arrow_down:
...bricks/koalas/tests/plot/test_frame_plot_plotly.py	23.33% <0.00%> (-76.67%)	:arrow_down:
...ricks/koalas/tests/plot/test_series_plot_plotly.py	26.92% <0.00%> (-71.26%)	:arrow_down:
databricks/koalas/usage_logging/__init__.py	28.20% <0.00%> (-64.36%)	:arrow_down:
databricks/koalas/usage_logging/usage_logger.py	47.82% <0.00%> (-52.18%)	:arrow_down:
databricks/koalas/__init__.py	74.39% <0.00%> (-14.64%)	:arrow_down:
databricks/conftest.py	89.09% <0.00%> (-10.91%)	:arrow_down:
databricks/koalas/typedef/typehints.py	84.42% <0.00%> (-10.56%)	:arrow_down:
databricks/koalas/spark/functions.py	88.88% <0.00%> (-7.41%)	:arrow_down:
... and 28 more

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[xinrong-meng]

Thanks for the fix! Since we have migrated Koalas to Apache Spark, would you like to port the fix to Spark instead?

[itholic]

I don't see any wired part in the docs https://koalas.readthedocs.io/en/latest/reference/api/databricks.koalas.DataFrame.plot.bar.html ??

Can you add before/after figure in the PR description when you find some time ??

[eavilaes]

Thanks for the fix! Since we have migrated Koalas to Apache Spark, would you like to port the fix to Spark instead?

Sure! Are these docs also on the Spark repository?

I don't see any wired part in the docs https://koalas.readthedocs.io/en/latest/reference/api/databricks.koalas.DataFrame.plot.bar.html ??

Can you add before/after figure in the PR description when you find some time ??

This is before the PR (notice same data being plotted on the first row):

And after the small modification: