metaclass conflict error on Python 2.7.12

[TheProdigyFilippo]

When running
from dj.choices import Choices

exception occurs:

...
return type.new(meta, classname, bases, classDict)
TypeError: Error when calling the metaclass bases
metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases

It is caused by using __metaclass__ in line 245 in __init__.py:

class Choices(six.with_metaclass(_ChoicesMeta, list)):                          
    __metaclass__ = _ChoicesMeta

Probably __metaclass__ is not needed when six.with_metaclass is used. Deleting __metaclass__ fixes the error

[mkurek]

Hi @TheProdigyFilippo - this behaviour has changed in six 1.11.0 (probably because of benjaminp/six#191), so if you want you can freeze six version at 1.10.0 or make PR to dj.choices with removing __metaclass__ property.

[konr4d]

@ambv This is a valid fix. (benjaminp/six#210) Could you please accept the pull request to avoid unnecessary forks?