Fixed Sentiment Analysis Dataset docs

[zacker150]

Currently, the __init__ documentation does not show up in the documentation for the Sentiment Analysis datasets. This PR fixes this issue.

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[codecov]

Codecov Report

Merging #1118 (4d3ce07) into master (742e1d3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1118   +/-   ##
=======================================
  Coverage   78.89%   78.89%           
=======================================
  Files          45       45           
  Lines        3090     3090           
=======================================
  Hits         2438     2438           
  Misses        652      652           

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