Use consistent naming for Django REST framework

[sliverc]

Description of the Change

This follows the naming DRF uses in its own documentation with an uppercase REST and all lowercase framework.

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 #977 (aa2924f) into master (7202f42) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #977   +/-   ##
=======================================
  Coverage   96.82%   96.82%           
=======================================
  Files          65       65           
  Lines        3904     3904           
=======================================
  Hits         3780     3780           
  Misses        124      124           

Impacted Files	Coverage Δ
rest_framework_json_api/settings.py	100.00% <ø> (ø)

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[n2ygk]

hmmm, I'd argue that DRF gets it wrong and the F should be Title case....