FIX add missing last image to snake dataset.
FIX add missing last image to snake dataset.

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