Django 2.0 support

[jonashaag]

Please see comment in code. We have to adapt to changes in Django (see https://github.com/django/django/commit/bfb746f983aa741afa3709794e70f1e0ab6040b5)

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@8e65892). Click here to learn what that means. The diff coverage is 92.3%.

@@            Coverage Diff            @@
##             master      #29   +/-   ##
=========================================
  Coverage          ?   98.66%           
=========================================
  Files             ?        6           
  Lines             ?      225           
  Branches          ?       48           
=========================================
  Hits              ?      222           
  Misses            ?        2           
  Partials          ?        1

Impacted Files	Coverage Δ
save_the_change/descriptors.py	100% <100%> (ø)
save_the_change/decorators.py	98.16% <85.71%> (ø)

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[jonashaag]

bump

[sonicsqwirl]

also bump

[jonashaag]

@karanlyons bump?

[jonashaag]

bump