fix(init): fix is_pre_commit_installed method

[Lee-W]

the logic of the original method is "pre_commit_not_installed"

Description

Closes #743

Checklist

• Add test cases to all the changes you introduce
• Run ./scripts/format and ./scripts/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

Run cz init and choose to install pre-commit hook without encountering error

Steps to Test This Pull Request

1. Run cz init
2. Choose to install pre-commit hook

Additional context

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: +0.04 🎉

Comparison is base (3cfed6d) 97.26% compared to head (eb39f8b) 97.31%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #744      +/-   ##
==========================================
+ Coverage   97.26%   97.31%   +0.04%     
==========================================
  Files          42       42              
  Lines        2045     2045              
==========================================
+ Hits         1989     1990       +1     
+ Misses         56       55       -1     

Flag	Coverage Δ
unittests	97.31% <66.66%> (+0.04%)	⬆️

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

Impacted Files	Coverage Δ
commitizen/commands/init.py	87.43% <50.00%> (ø)
commitizen/__version__.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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