small edit, for extracting dfe-alpha output

[chriscrsmith]

At some point we must have changed the dfe-alpha command without updating L350 for extracting the output. Here's an example output file:

cat results/inference/OutOfAfrica_3G09/DFE-alpha/Gamma_H17/ensembl_havana_104_exons/1845187043/chr21/pop0/nonneu/est_dfe.out
N1 100 N2 131 t2 106.0000 Nw 110.32 b 99.9999 Es -0.008198 f0 0.000000000 L -2599.8524