fix: categorical parameter regression on dense dataset caused by missing whitespace

[imatiach-msft]

fix for categorical parameter regression on dense dataset caused by missing whitespace

fixes issue #900

[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #909 into master will decrease coverage by 0.71%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #909      +/-   ##
==========================================
- Coverage   83.92%   83.20%   -0.72%     
==========================================
  Files         189      189              
  Lines        8769     8769              
  Branches      558      558              
==========================================
- Hits         7359     7296      -63     
- Misses       1410     1473      +63     

Impacted Files	Coverage Δ
...om/microsoft/ml/spark/lightgbm/LightGBMUtils.scala	95.29% <100.00%> (+3.52%)	⬆️
...crosoft/ml/spark/vw/featurizer/MapFeaturizer.scala	0.00% <0.00%> (-100.00%)	⬇️
...soft/ml/spark/vw/featurizer/StringFeaturizer.scala	0.00% <0.00%> (-100.00%)	⬇️
...oft/ml/spark/vw/featurizer/NumericFeaturizer.scala	0.00% <0.00%> (-100.00%)	⬇️
...ml/spark/vw/featurizer/StringArrayFeaturizer.scala	0.00% <0.00%> (-100.00%)	⬇️
...soft/ml/spark/vw/featurizer/VectorFeaturizer.scala	0.00% <0.00%> (-90.00%)	⬇️
...crosoft/ml/spark/vw/VowpalWabbitInteractions.scala	3.03% <0.00%> (-87.88%)	⬇️
.../microsoft/ml/spark/vw/VowpalWabbitBaseModel.scala	36.58% <0.00%> (-58.54%)	⬇️
...microsoft/ml/spark/vw/VowpalWabbitClassifier.scala	51.51% <0.00%> (-39.40%)	⬇️
...oft/ml/spark/vw/VowpalWabbitMurmurWithPrefix.scala	34.14% <0.00%> (-36.59%)	⬇️
... and 26 more

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