bump version to 0.3.1 to reference spark 2.0.0 fix
bump version to 0.3.1 to reference spark 2.0.0 fix

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