Set release version to 2.3.0.

[mblayman]

Fixes #382

[codecov-io]

Codecov Report

Merging #383 into develop will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           develop     #383   +/-   ##
========================================
  Coverage    93.13%   93.13%           
========================================
  Files           52       52           
  Lines         2693     2693           
========================================
  Hits          2508     2508           
  Misses         185      185

Impacted Files	Coverage Δ
rest_framework_json_api/__init__.py	100% <100%> (ø)	⬆️

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