Fix for isort>4.3.10.

[carltongibson]

No description provided.

[codecov-io]

Codecov Report

Merging #1055 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1055   +/-   ##
=======================================
  Coverage   98.34%   98.34%           
=======================================
  Files          15       15           
  Lines        1205     1205           
=======================================
  Hits         1185     1185           
  Misses         20       20

Impacted Files	Coverage Δ
django_filters/rest_framework/__init__.py	100% <100%> (ø)	⬆️
django_filters/rest_framework/backends.py	94.59% <100%> (ø)	⬆️
django_filters/__init__.py	93.75% <100%> (ø)	⬆️

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