Support for `quantile` distribution in GBM

[zhengwei14]

INFO 2021-10-29 16:26:52 [main] org.jpmml.h2o.Main [TID: N/A]- Loading MOJO..
INFO 2021-10-29 16:26:52 [main] org.jpmml.h2o.Main [TID: N/A]- Loaded MOJO in 305 ms.
INFO 2021-10-29 16:26:52 [main] org.jpmml.h2o.Main [TID: N/A]- Converting MOJO to PMML..
ERROR 2021-10-29 16:26:53 [main] org.jpmml.h2o.Main [TID: N/A]- Failed to convert MOJO to PMML
java.lang.IllegalArgumentException: Distribution family quantile is not supported
at org.jpmml.h2o.GbmMojoModelConverter.encodeModel(GbmMojoModelConverter.java:111)
at org.jpmml.h2o.GbmMojoModelConverter.encodeModel(GbmMojoModelConverter.java:45)
at org.jpmml.h2o.Converter.encodePMML(Converter.java:88)
at org.jpmml.h2o.Main.run(Main.java:120)
at org.jpmml.h2o.Main.main(Main.java:90)