ENH: added mpi4py to travis
ENH: added mpi4py to travis

mnicholl/MOSFiT,villrv/MOSFiT,guillochon/MOSFiT,guillochon/MOSFiT,villrv/MOSFiT,bmockler/MOSFiT,guillochon/MOSFiT,bmockler/MOSFiT,mnicholl/MOSFiT,mnicholl/MOSFiT,guillochon/FriendlyFit