Fix MultiIndex.to_pandas() and __repr__().

[ueshin]

Resolves #805.

[codecov-io]

Codecov Report

Merging #832 into master will decrease coverage by 0.04%.
The diff coverage is 81.25%.

@@            Coverage Diff             @@
##           master     #832      +/-   ##
==========================================
- Coverage   94.35%   94.31%   -0.05%     
==========================================
  Files          32       32              
  Lines        5883     5893      +10     
==========================================
+ Hits         5551     5558       +7     
- Misses        332      335       +3

Impacted Files	Coverage Δ
databricks/koalas/series.py	95.22% <ø> (ø)	⬆️
databricks/koalas/indexes.py	97.12% <81.25%> (-2.11%)	⬇️

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[HyukjinKwon]

LGTM

[softagram-bot]

Softagram Impact Report for pull/832 (head commit: ab8f7d1)

⭐ Change Overview

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💡 Insights

• Co-change Alert: You modified test_dataframe.py. Often frame.py (databricks/koalas) is modified at the same time.

📄 Full report

• Permalink: Full report for pull/832

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