Removed a word from export_bng docstring
Removed a word from export_bng docstring

neurord/pysb,LoLab-VU/pysb,d-fan/pysb,johnbachman/pysb,neurord/pysb,spgarbet/pysb,neurord/pysb,jmuhlich/pysb,alubbock/pysb,d-fan/pysb,pysb/pysb,spgarbet/pysb,d-fan/pysb,johnbachman/pysb,spgarbet/pysb,LoLab-VU/pysb