Use six.text_type instead of unicode

[jaredlockhart]

Should the following two lines:

https://github.com/clouserw/tower/blob/master/tower/__init__.py#L55-L56

use six.text_type instead of unicode like here:

https://github.com/django/django/blob/master/django/utils/translation/__init__.py#L99

?

[clouserw]

Probably! I swapped it out and ran the tests and it still worked fine. I don't know a lot about six so I'm not sure when it would be a good idea to do it. Any advice?