BUG: fix the Frequency Response plot of Flight class

[Gui-FernandesBR]

Pull request type

• [x] Code changes (bugfix, features)

Checklist

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

Current behavior

New behavior

Breaking change

• [x] No

Additional information

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.