added fibonacci using formula along with test cases

[dev-madhurendra]

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Describe your change:

I added a code which calculates the nth fibonacci number using formula in a very less time.

• [ ✅ ] Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• [ ✅ ] I have read CONTRIBUTING.md.
• [ ✅ ] This pull request is all my own work -- I have not plagiarized.
• [ ✅ ] I know that pull requests will not be merged if they fail the automated tests.
• [ ✅ ] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [ ✅ ] All new JavaScript files are placed inside an existing directory.
• [ ✅ ] All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• [ ✅ ] All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• [ ✅ ] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[appgurueu]

Please add this to the existing Fibonacci.js file (and add the tests to the corresponding test file). Use a proper JSDoc comment. Also, use each for the test cases.

The formula doesn't need to be a comment, that's redundant with the implementation (also, the formula in the comment seems to differ from the one you implemented?). You can use x**y instead of Math.pow(x, y). Note also that Wikipedia suggests a slightly simpler formula for computation by rounding.

Side note: I find calling this O(1) time/space complexity slightly misleading; this is only (trivially) given because the numbers involved have constant size. If this were to use bigints / bigdecimals, it wouldn't be constant time anymore.

[dev-madhurendra]

@appgurueu When I'll be able to merge this PR ?

[appgurueu]

@appgurueu When I'll be able to merge this PR ?

It's still waiting on a second review from @raklaptudirm.

[raklaptudirm]

Sorry for the late review, but consider adding a resource to the formula used here.