Switch to Clinton's fork of django-waffle

[thallada]

Switching to @clintonb's fork of django-waffle, which has an open pull request against the main repo. Clinton's fork is more well-tested than the other fork we were on.

Hopefully this is only temporary and once the status of django-waffle is figured out, we can go back to installing from pip.

@edx/educator-dahlia

[clintonb]

I will not guarantee my fork will exist for any period of time after my PR is merged (if it's ever merged!). Please fork this to edX. In general, anytime we need to pull from GitHub, we should be pulling from either the official repo or an edX repo.

[codecov-io]

Codecov Report

Merging #693 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #693   +/-   ##
======================================
  Coverage    94.2%   94.2%           
======================================
  Files         184     184           
  Lines        9381    9381           
  Branches      742     742           
======================================
  Hits         8837    8837           
  Misses        380     380           
  Partials      164     164

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[thallada]

We should switch to django-waffle version 0.12.0 from pip instead now that Clinton has become a maintainer and merged his PR (see jazzband/django-waffle#246)