Drop support for Python 3.4

[dennissiemensma]

This is blocking for #510.

"Django 2.1 supports Python 3.5, 3.6, and 3.7. Django 2.0 is the last version to support Python 3.4. We highly recommend and only officially support the latest release of each series."

And Python 3.4 will be supported until early next year, so at least six months.

"There are no specific plans for the next release of Python 3.4. However, the expectation is that Python 3.4.10 will be released in March of 2019, and this will be the final release of Python 3.4."

TODO

• Update Travis
• Update docs
• Update Python version in Github

[dennissiemensma]

I will push this for the next release, because I found out I've done the same thing with python 3.3.

It was end of life September 2017. I stopped supporting it almost a year before because of Django 1.9, on January 2017.

[dennissiemensma]

Merged to development.

[dennissiemensma]

I will allow Python 3.4 for a few more months, but I'll keep it unsupported.

[dennissiemensma]

Will be released with #616.