cater for changed API in Django 1.11

[nschlemm]

as mentioned on https://docs.djangoproject.com/en/1.11/releases/1.11/#database-backend-api:
"The name keyword argument is added to the DatabaseWrapper.create_cursor(self, name=None) method to allow usage of server-side cursors on backends that support it."
(currently only postgresql)

also adjusted tox.ini and .travis.yml to consider the currently supported versions

[nschlemm]

Fixes #16

[coveralls]

Coverage decreased (-4.9%) to 62.385% when pulling 8360856 on nschlemm:django-1.11-compatibility into 7215fcd on snowball-one:master.

[coveralls]

Coverage decreased (-4.7%) to 62.609% when pulling dc65410 on nschlemm:django-1.11-compatibility into 7215fcd on snowball-one:master.

[coveralls]

Coverage decreased (-4.7%) to 62.609% when pulling dc65410 on nschlemm:django-1.11-compatibility into 7215fcd on snowball-one:master.

[coveralls]

Coverage decreased (-4.7%) to 62.609% when pulling dc65410 on nschlemm:django-1.11-compatibility into 7215fcd on snowball-one:master.

[xordoquy]

Hi there.

First, thanks for the great software ! Nice to see there's already a port to Django 1.11.
Any idea if/when this will be merged and released ? We require this PR to upgrade projects to Django 1.11

[dbaty]

Hi @nschlemm , we (Polyconseil) have taken over the maintenance of django-cid (with the nice support of the original author). I have started to clean up pull requests and modernize the project.

Your pull request had changes which should be reflected in the following commits:

• ac607f3 fixes the support of Django 1.11 for database backends;
• 4476392 fixes the generation of the cid when the middleware is not used.

I see that you also wanted to clean up MIDDLEWARE vs. MIDDLEWARE_CLASS. That's a good idea. I have decided to drop the support of versions <1.11, which will let us do that even more cleanly.

Feel free to contribute again if you feel like it. We use django-cid and are committed to maintain it.