Issue 135 all zeros one hot vectors

[fealho]

Resolves #135.

[codecov-io]

Codecov Report

Merging #136 (a34b6e3) into master (3ee57fd) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #136      +/-   ##
==========================================
+ Coverage   98.61%   98.63%   +0.01%     
==========================================
  Files           9        9              
  Lines         434      438       +4     
==========================================
+ Hits          428      432       +4     
  Misses          6        6              

Impacted Files	Coverage Δ
rdt/transformers/categorical.py	95.65% <100.00%> (+0.19%)	⬆️
rdt/hyper_transformer.py	100.00% <0.00%> (ø)

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