account for changes to the LDA method in Spark 3.0
account for changes to the LDA method in Spark 3.0

Signed-off-by: Yitao Li <506e136862ca6a2cd6209c2ab7376874a235e7c2@rstudio.com>

rstudio/sparklyr,rstudio/sparklyr,rstudio/sparklyr,rstudio/sparklyr