Add future==0.16.0 as a dependency since it's required by CloudML SDK (…

…#143)

As of the latest release of CloudML Python SDK, that package seems to require future==0.16.0, so until it's fixed, we'll take it as a dependency.

setup.py

@@ -91,7 +91,7 @@
 for accessing Google's Cloud Platform services such as Google BigQuery.
  """,
  install_requires=[
- 'future==0.15.2',
+ 'future==0.16.0',
  'futures==3.0.5',
  'google-cloud==0.19.0',
  'google-api-python-client==1.5.1',