Update of django, drf, python version handling in tox.ini

[angvp]

• Removed tests for drf 2.4, 3.0 because django versions 1.8,1.9,1.10 doesn't play well with them.
• Untie drf and django to specific releases for a version, and instead get the latest release of every version

Some of these changes were done in #252 but weren't merged because #256 was more complete adding support of drf3.4 and django 1.10, however I rather like to test against the latest release of a version so this is the main motivation of this PR.

Regards.

[angvp]

Closing it because it got no interest from the maintainers.

Note to the maintainers: Please drop some feedback to ALL the PR that you have open, merge, reject them or whatever but give feedback, the standby status is the worst part.

[jpadilla]

@angvp definitely interested, just a bit caught up in work. Should be able to catch up with issues and pull requests for this project soon. Thanks for the reminder.

As a note, anyone that wants to step up and help out with maintenance will be greatly welcome.

[angvp]

Count me in!

[jpadilla]

@angvp awesome, thanks! just sent out an invite. Unfortunately Travis CI is still having issues after AWS outage so I can't see what's failing now here after my resolve. Will wait it out.

[angvp]

@jpadilla Can you re run travis on this pr? thanks!

[jpadilla]

@angvp green :)

[jpadilla]

Just released this under v1.10. Thank you @angvp!