Add Travis CI build

[johnthagen]

It would help give better confidence which Python versions the project works on if there was some automated CI builds. I'm happy to create one, but https://travis-ci.org/teddziuba/django-sslserver needs to be activated first. @battlemidget are you able to do that?

[adam-stokes]

I'll check and see

[adam-stokes]

Looks like I don't have sufficient access, I'll email Ted and see if I can get that enabled

[adam-stokes]

@teddziuba is it possible to get us connected to travis-ci?

[johnthagen]

Reference CI configuration from another Django plugin project:

• https://github.com/beda-software/drf-writable-nested/blob/master/.travis.yml
• https://github.com/beda-software/drf-writable-nested/blob/master/tox.ini

[johnthagen]

Travis CI (.com) is no longer free for FOSS projects so closing this issue.