Fix rawPrediction of OpXGBoostClassifcationModel for binary classification

[kinfaikan]

Related issues
NA

Describe the proposed solution
OpXGBoostClassificationModel outputs only one raw prediction value for binary classification and causes ArrayIndexOutOfBoundsException in BinaryClassificationEvaluator. Modify OpXGBoostClassificationModel to generate two raw prediction values for binary classification.

Describe alternatives you've considered
NA

Additional context
NA

[codecov]

Codecov Report

Merging #229 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #229      +/-   ##
==========================================
- Coverage   86.41%   86.39%   -0.02%     
==========================================
  Files         312      312              
  Lines       10182    10183       +1     
  Branches      333      564     +231     
==========================================
- Hits         8799     8798       -1     
- Misses       1383     1385       +2

Impacted Files	Coverage Δ
...ages/impl/classification/OpXGBoostClassifier.scala	32.75% <100%> (+1.17%)	⬆️
...es/src/main/scala/com/salesforce/op/OpParams.scala	85.71% <0%> (-4.09%)	⬇️

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[oleksii-nikitchuk]

Hey @tovbinm do you have a plan to release this fix?

[tovbinm]

Yes, we are planning to make a release within the next few weeks.

For now, you can publish from master locally.