allow 'n = Inf' for collect on Spark DF
allow 'n = Inf' for collect on Spark DF

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