Fix json decoding on Python 3

Related to #36 -- there exists a much easier solution to the approach taken there, that is just relying on the `requests` library to decode the json (the Python 2/3 difference is dealt with there already).

How can the current implementation even pass the tests on Python 3? The `get_database_list` CAN'T possibly work on Python 3 because it wasn't taken care of in #36.
The function used to return a dict ant it now returns a string (json)
You should return ``` json.loads(response.json())```