Improve version comparison

[iago1460]

The current string comparison doesn't work with django 1.10 version and in other cases.

I am using the parse_version function defined in setuptools to solve this.

[nemesifier]

Travis build fails and commit author is not set.

[nemesifier]

Thanks

[iago1460]

Thank you , I didn't have time to fix it.

By the way I publish a package extending this library https://github.com/iago1460/django-dynamic-fields maybe it's useful for someone.