BUG: fix the Frequency Response plot of Flight class

[Gui-FernandesBR]

Pull request type

• Code changes (bugfix, features)

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior

New behavior

Breaking change

• No

Additional information

• I noticed it was just a matplotlib plotting matter, not a problem with the calculations.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.94%. Comparing base (aa0673a) to head (7e2c6bf).
Report is 11 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #653      +/-   ##
===========================================
+ Coverage    75.75%   75.94%   +0.19%     
===========================================
  Files           81       85       +4     
  Lines         9820    10082     +262     
===========================================
+ Hits          7439     7657     +218     
- Misses        2381     2425      +44     

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