update the header when slicing
update the header when slicing

keflavich/pyspeckit,pyspeckit/pyspeckit,allisony/pyspeckit,keflavich/pyspeckit,low-sky/pyspeckit,jpinedaf/pyspeckit,low-sky/pyspeckit,e-koch/pyspeckit,allisony/pyspeckit,vlas-sokolov/pyspeckit,jpinedaf/pyspeckit,vlas-sokolov/pyspeckit,pyspeckit/pyspeckit,e-koch/pyspeckit