Python 2.7 support

[simra]

Hi, a small suggestion to add a line to the DPSU spark implementation, to support down-level python:
from __future__ import division

https://github.com/opendifferentialprivacy/whitenoise-samples/blob/332d7ef7c4fcf811995f9e6a3aab8d8f4c298a88/data/policy_laplace.py#L1

Without the change, initializing PolicyLaplace incorrectly applies integer division in a few spots.

[raprasad]

Thanks*, @simra
(Much delayed)

[joshua-oss]

Completely missed this. Great suggestion; I have patched it in #95