Update positional_only.py

tests/instantiate/positional_only.py

@@ -1,7 +1,7 @@
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
 from typing import Any
 
-# Contains Python 3.8 syntax, disable mypy on Python 3.6 will fail to parse it normally.
+# Contains Python 3.8 syntax, mypy on Python < 3.8 will fail to parse it normally.
 # To work around it, the code is executed as string instead of as good old class.
 
 text = """