spark-package does not specify future as a dependency

[falaki]

After a fresh install of spark-package through pip, I was getting this error:

$ spark-package 
Traceback (most recent call last):
  File "/usr/local/bin/spark-package", line 7, in <module>
    from spark_package.spark_package import main
  File "/home/hossein/.local/lib/python2.7/site-packages/spark_package/spark_package.py", line 31, in <module>
    from builtins import input
ImportError: No module named builtins

And then running pip install future resolved the issue.

Environment:

$ python --version
Python 2.7.12

cc @brkyvz