fixing typos #3

I just randomly find these by the way. Good work on the framework!

Author: maciejdomagala

qlib/contrib/strategy/strategy.py

@@ -30,7 +30,7 @@ def generate_order_list(self, score_series, current, trade_exchange, pred_date,
 
         Parameters
         -----------
-        score_series : pd.Seires
+        score_series : pd.Series
             stock_id , score.
         current : Position()
             current state of position.