Sarina/fix underscore resource

@singingwolfboy @louyihua this is necessary for the transifex pull commands to work.


Really? This file is generated after ```extraction``` step, why can it cause the ```i18n/generate.py``` script to fail?
But I do see that only the unsplitted version of ```underscore.po``` was uploaded to the transifex.com, so maybe this is the actual cause?