Adding lxml requirement
Adding lxml requirement


Former-commit-id: a786d54ea7917e4d1ffcf888f783c5788d15d6a7
travs/PyOpenWorm,openworm/PyOpenWorm,gsarma/PyOpenWorm,kaustubhcs/PyOpenWorm,hnunner/PyOpenWorm,openworm/PyOpenWorm,gsarma/PyOpenWorm