Add version to scipy dependency

[jamescasbon]

Hi, which version of scipy is needed please? Ideally this should be in setup.py

I get a fail with

ImportError: cannot import name invwishart

[RJT1990]

Hi James - yes version requirements are indeed important and it's a bad omission on my part; the reason why I haven't got around to specifying these yet as I wanted to finalize a list of requirements for the beta release, which is scheduled in next few months. Scipy versions >= 0.17.1 should work for now.