Added BellmanFord

[Mayank17M]

Welcome to JavaScript community

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Describe your change:

• 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 its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[Mayank17M]

@raklaptudirm Please check if it is appropriate now. Thanks!

[raklaptudirm]

Please use standard.js to style your code.

[raklaptudirm]

All looks good. I should suggest moving the tests into a separate jest file in the test/ sub directory. You can refer to the other test files if you need so. If you do not feel like doing it, this code is also acceptable, but it will be better if you move the tests.