fix travis build: can't conda-install spectral-cube
fix travis build: can't conda-install spectral-cube

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