Update docs to entityset for wordcount primitive example

[RogerTangos]

• corrects an error in the WordCount example in the docs
• WordCount example now gives the expected result

[codecov]

Codecov Report

Merging #368 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #368   +/-   ##
=======================================
  Coverage   95.33%   95.33%           
=======================================
  Files          86       86           
  Lines        8032     8032           
=======================================
  Hits         7657     7657           
  Misses        375      375

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[kmax12]

Looks good merging