Enable tests for Django 2.1 and add classifier

[blueyed]

No description provided.

[codecov-io]

Codecov Report

Merging #614 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #614   +/-   ##
=======================================
  Coverage   92.19%   92.19%           
=======================================
  Files          33       33           
  Lines        1705     1705           
  Branches      143      143           
=======================================
  Hits         1572     1572           
  Misses         95       95           
  Partials       38       38

Flag	Coverage Δ
#dj110	84.28% <ø> (ø)	⬆️
#dj111	86.39% <ø> (ø)	⬆️
#dj18	84.98% <ø> (-0.12%)	⬇️
#dj19	84.16% <ø> (ø)	⬆️
#dj20	84.57% <ø> (ø)	⬆️
#dj21	84.57% <ø> (?)
#djmaster	84.57% <ø> (ø)	⬆️
#mysql_innodb	84.57% <ø> (ø)	⬆️
#mysql_myisam	84.51% <ø> (ø)	⬆️
#postgres	87.97% <ø> (ø)	⬆️
#py27	89.56% <ø> (ø)	⬆️
#py34	84.16% <ø> (ø)	⬆️
#py35	84.28% <ø> (ø)	⬆️
#py36	85.04% <ø> (ø)	⬆️
#sqlite	86.39% <ø> (ø)	⬆️
#sqlite_file	84.16% <ø> (ø)	⬆️

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