Fix conventional commits schema pattern

[shifqu]

Description

Adjust schema_pattern in cz_conventional_commits to match the conventional_commits spec

Checklist

• Add test cases to all the changes you introduce
• Run ./script/format and ./script/test locally to ensure this change passes linter check and test
• Test the changes on the local machine manually
• Update the documentation for the changes

Expected behavior

• cz -n cz_conventional_commits check -m "feat!(scope): message" to fail validation
• cz -n cz_conventional_commits check -m "feat(scope)!: message" to pass validation

Steps to Test This Pull Request

1. Check out this branch
2. Run commands as described in "Expected behaviour"

Additional context

#381

[codecov]

Codecov Report

Merging #382 (e107411) into master (8638512) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #382      +/-   ##
==========================================
+ Coverage   97.60%   97.67%   +0.07%     
==========================================
  Files          39       39              
  Lines        1378     1378              
==========================================
+ Hits         1345     1346       +1     
+ Misses         33       32       -1     

Flag	Coverage Δ
unittests	97.67% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...en/cz/conventional_commits/conventional_commits.py	100.00% <ø> (+1.58%)	⬆️
commitizen/__version__.py	100.00% <100.00%> (ø)

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