Bumped versions to Spark 0.9.1

Self explanatory!

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #190 from tdas/branch-0.9-version-bump and squashes the following commits:

34576ee [Tathagata Das] Bumped versions to Spark 0.9.1
Removed incubating from Spark version in all the pom.xml.