Update datastax to 2.0.1, fixes wrong dependency in maven central.

The build.gradle depended on the cassandra-driver-core 1.0.0 which
broke my application with a
  `ClassNotFoundException: com.datastax.driver.core.Query`

A bit weird is that the pom.xml (at http://repo1.maven.org/maven2/com/streamsend/pillar/1.0.2/pillar-1.0.2.pomhttp://repo1.maven.org/maven2/com/streamsend/pillar/1.0.2/pillar-1.0.2.pom) specifies 1.0.2 - no clue where this is coming
from. Still, the 1.x version seems wrong.
Merge pull request #4 from magro/update-datastax-driver

Update datastax to 2.0.1, fixes wrong dependency in maven central.