update NEWS.md for sparklyr 1.5 release (#2797)
update NEWS.md for sparklyr 1.5 release (#2797)

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