updates the Django version and changes the operator to ~= in order to allow compatible versions

[azneto]

This pull request addresses issue #321

I hereby agree to licence this and any previous contributions under
the terms of the GNU General Public License version 3 as published by
the Free Software Foundation

I have read the CONTRIBUTING.rst file and understand that
TravisCI will be used to confirm the tests and flake8 style
checks pass with these changes.

I am happy be thanked by name in the CONTRIB.rst files,
and have added myself to the file as part of this pull request.
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[codecov-commenter]

Codecov Report

Merging #322 (2aabd64) into master (217ac14) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #322   +/-   ##
=======================================
  Coverage   69.11%   69.11%           
=======================================
  Files          30       30           
  Lines        4037     4037           
  Branches      229      229           
=======================================
  Hits         2790     2790           
  Misses       1188     1188           
  Partials       59       59           

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