Added django 2.2 support

[lino]

tox tests are passing

[zsoldosp]

Hi @lino, thanks for the PR, it looks good to me! :+1:

When new releases are made, the following changes also should happen

• bump the version in django_currentuser/__init__.py - in this case, only the build number (last) needs to increase, as no API changes or features were introduced/removed
• update .travis.yml - just running tox2travis.py should take care of that (or maybe need to pipe the output into .travis.yml)
• update the README.md with release notes - however, as I see it has been, ahem, a bit behind so we should catch up on that

However, I recall that for releases there was a problem with 3.7 python recently, cc'ing @kairichard and @Eorhim for input on that

[Eorhim]

@lino, @zsoldosp

The problem with Python 3.7 was solved in fe951cf6807beb9671734a2a13ffb07391fa7a81 by cutting out some outdated build system and using the Travis functionality directly.

Unfortunately tox2travis.py wasn't updated. So if you want to use that script to generate the .travis.yml configuration, you will loose the packaging ability.

[Eorhim]

@lino: I close this pull request, because I extended your work in pull request #29.

Thank you for pushing the project forward with your work.