chore: fix comment typos in `fibonacci.rs`

[y5c4l3]

Pull Request Template

Description

Fix comment typos in fibonacci.rs.

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] I ran bellow commands using the latest version of rust nightly.
• [x] I ran cargo clippy --all -- -D warnings just before my last commit and fixed any issue that was found.
• [x] I ran cargo fmt just before my last commit.
• [x] I ran cargo test just before my last commit and all tests passed.
• [x] I checked COUNTRIBUTING.md and my code follows its guidelines.

Please make sure that if there is a test that takes too long to run ( > 300ms), you #[ignore] that or try to optimize your code or make the test easier to run. We have this rule because we have hundreds of tests to run; If each one of them took 300ms, we would have to wait for a long time.

[codecov-commenter]

Codecov Report

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

Project coverage is 95.41%. Comparing base (1b07a48) to head (2932dee). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #827 +/- ## ======================================= Coverage 95.41% 95.41% ======================================= Files 314 314 Lines 22754 22754 ======================================= Hits 21710 21710 Misses 1044 1044 ```

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