require relatively recent sklearn, add scipy requirement.
require relatively recent sklearn, add scipy requirement.

pystruct/pystruct,d-mittal/pystruct,amueller/pystruct,wattlebird/pystruct,amueller/pystruct,massmutual/pystruct,d-mittal/pystruct,pystruct/pystruct,wattlebird/pystruct,massmutual/pystruct