renamed exp_mat to expression matrix
renamed exp_mat to expression matrix

ryi06/inferelator_ng,simonsfoundation/inferelator_ng,simonsfoundation/inferelator_ng,AaronWatters/inferelator_ng,ryi06/inferelator_ng,simonsfoundation/inferelator_ng,AaronWatters/inferelator_ng,AaronWatters/inferelator_ng