fix: remove six dependency

[dpgaspar]

Remove unneeded six dependency

Fixes: #83

[codecov-commenter]

Codecov Report

Merging #84 (8be5088) into master (742f590) will decrease coverage by 0.00%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master      #84      +/-   ##
==========================================
- Coverage   94.41%   94.40%   -0.01%     
==========================================
  Files          15       15              
  Lines         967      966       -1     
==========================================
- Hits          913      912       -1     
  Misses         54       54              

Flag	Coverage Δ
python	94.40% <50.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
es/baseapi.py	89.87% <50.00%> (-0.07%)	⬇️

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