Hotfix- CODE_CHALLENGE instead of CODE_VERIFIER in docs

[matiseni51]

Fixes #1207

Description of the Change

code_challenge_method=S256 in authorize call added in getting_started documentation

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

[n2ygk]

@matiseni51 please fill out the pull request template (not sure how that got missed) and add it to the description.

[codecov]

Codecov Report

Merging #1208 (d95d218) into master (9383e08) will decrease coverage by 0.81%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1208      +/-   ##
==========================================
- Coverage   96.85%   96.04%   -0.82%     
==========================================
  Files          31       26       -5     
  Lines        1813     1314     -499     
==========================================
- Hits         1756     1262     -494     
+ Misses         57       52       -5     

Impacted Files	Coverage Δ
oauth2_provider/admin.py
oauth2_provider/models.py
oauth2_provider/settings.py
oauth2_provider/urls.py
oauth2_provider/__init__.py

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[matiseni51]

@n2ygk sorry, my bad.

[n2ygk]

Thanks!