Lock whitenoise dependency version

[Carles-Figuerola]

Whitenoise starting at 5.0.0 (10/12/2019) does not support python2.7 anymore and fails building. Locking to latest version that supports python2.7

https://pypi.org/project/whitenoise/5.0/

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@0aacb4c). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #2606   +/-   ##
=========================================
  Coverage          ?   80.21%           
=========================================
  Files             ?       87           
  Lines             ?     9335           
  Branches          ?     1988           
=========================================
  Hits              ?     7488           
  Misses            ?     1564           
  Partials          ?      283           

Impacted Files	Coverage Δ
webapp/graphite/readers/rrd.py	86.15% <0.00%> (ø)
webapp/graphite/metrics/urls.py	100.00% <0.00%> (ø)
webapp/graphite/browser/views.py	67.33% <0.00%> (ø)
webapp/graphite/dashboard/models.py	90.00% <0.00%> (ø)
webapp/graphite/readers/__init__.py	100.00% <0.00%> (ø)
webapp/graphite/account/admin.py	100.00% <0.00%> (ø)
webapp/graphite/render/urls.py	100.00% <0.00%> (ø)
webapp/graphite/app_settings.py	70.96% <0.00%> (ø)
webapp/graphite/render/datalib.py	96.38% <0.00%> (ø)
webapp/graphite/worker_pool/pool.py	100.00% <0.00%> (ø)
... and 77 more

---

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 0aacb4c...65d986e. Read the comment docs.

[ploxiln]

A slightly more complete version of this change showed up just recently in a different open PR: e18778d in #2409

[Carles-Figuerola]

Happy to close this one!