fix for cli loaded metrics

[scopatz]

Small and simple.

[scopatz]

For @opotowsky

[opotowsky]

Thanks so much for your quick attention @scopatz!
Alas, after a clean build, I still get the same error as before:

File "./test_cym.py", line 10, in
f2 = evaler.eval('MaterialsSquared')
File "/home/opotowsky/.local/lib/python2.7/site-packages/cymetric/evaluator.py", line 72, in eval
d = d.add_val(m.schema.byte_names[field], rawd[str(field)][i],
KeyError: 'MassSquared'
Segmentation fault (core dumped)

[opotowsky]

All looks great, thanks again @scopatz