Pin django-debug-toolbar version to fix Python 2.7 tests

[sliverc]

Description of the Change

Pin django debug toolbar to fix tests in master.

This is a quick fix and at a later point we should try to avoid having debug toolbar as dependency for tests. A bit more complicated to fix as example and tests are combined.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #634 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #634   +/-   ##
=======================================
  Coverage   95.66%   95.66%           
=======================================
  Files          56       56           
  Lines        2861     2861           
=======================================
  Hits         2737     2737           
  Misses        124      124

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update db5cd72...2fdd4d3. Read the comment docs.

[n2ygk]

Ah, I see it was pinned in requirements-development.txt but not here. LGTM.