Fix example.urls to work with Django 2.0

[jdufresne]

Fixes unhandled exception:

django.core.exceptions.ImproperlyConfigured: Passing a 3-tuple to include() is not supported. Pass a 2-tuple containing the list of patterns and app_name, and provide the namespace argument to include() instead.

[codecov]

Codecov Report

Merging #1034 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1034   +/-   ##
=======================================
  Coverage   84.15%   84.15%           
=======================================
  Files          24       24           
  Lines        1294     1294           
  Branches      176      176           
=======================================
  Hits         1089     1089           
  Misses        156      156           
  Partials       49       49

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[matthiask]

Thanks!