MAINT: Fixes DataPortal.get_spot_value to correctly handle 'price' field
MAINT: Fixes DataPortal.get_spot_value to correctly handle 'price' field

Querying for the price field of an equity actually looks at the close
field, so we should do the same for futures. Otherwise `data.can_trade`
and `data.current` of 'price' fail for futures.

alphaBenj/zipline,florentchandelier/zipline,magne-max/zipline-ja,bartosh/zipline,humdings/zipline,magne-max/zipline-ja,alphaBenj/zipline,enigmampc/catalyst,enigmampc/catalyst,humdings/zipline,Scapogo/zipline,quantopian/zipline,quantopian/zipline,bartosh/zipline,Scapogo/zipline,florentchandelier/zipline