Fix security issue pointed by Ivan

generation/generator.py

@@ -16,7 +16,7 @@ class Generator(object):
 
     def __init__(self, args, keys=None):
         self.args = args
-        self.keys = keys
+        self.__keys = keys
         self.current_key_id = 0
 
         # if the args provided, will initialize with the prompt builder for full usage