json encoding support for python 3.9

[emrahcetiner]

encoding argument deprecated in json library since python 3.1 and it will be removed in python 3.9.

https://docs.python.org/3/library/json.html#json.loads

json.loads(s, *, cls=None, object_hook=None, parse_float=None, parse_int=None, parse_constant=None, object_pairs_hook=None, **kw)
Deserialize s (a str, bytes or bytearray instance containing a JSON document) to a Python object using this conversion table.
The other arguments have the same meaning as in load(), except encoding which is ignored and deprecated since Python 3.1.
If the data being deserialized is not a valid JSON document, a JSONDecodeError will be raised.
Deprecated since version 3.1, will be removed in version 3.9: encoding keyword argument.
Changed in version 3.6: s can now be of type bytes or bytearray. The input encoding should be UTF-8, UTF-16 or UTF-32.

[emrahcetiner]

I have submitted a pull request for this issue. #20