Fix docstring in TradingEnvironment class
Fix docstring in TradingEnvironment class

quantopian/zipline,florentchandelier/zipline,florentchandelier/zipline,bartosh/zipline,alphaBenj/zipline,Scapogo/zipline,bartosh/zipline,humdings/zipline,enigmampc/catalyst,enigmampc/catalyst,quantopian/zipline,Scapogo/zipline,humdings/zipline,alphaBenj/zipline