Fix syntax error

chatbot_constructor.py

@@ -17,7 +17,7 @@ os.mkdir("cache")
 class ValueConstraint(Constraint):
     def __init__(self, min_value: float = -1, max_value: float = 1):
         self.min_value = min_value
-        self.max_value
+        self.max_value = max_value
 
     def __call__(self, w):
         return K.clip(w, self.min_value, self.max_value)