feat: Added digital root algorithm(also with recursion)

[ankana2113]

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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 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: #1747 .

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 34 lines in your changes missing coverage. Please review.

Project coverage is 84.61%. Comparing base (55ff0ad) to head (968cf29).

Files with missing lines	Patch %	Lines
Maths/DigitalRoot.js	0.00%	34 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1754      +/-   ##
==========================================
- Coverage   84.76%   84.61%   -0.15%     
==========================================
  Files         378      379       +1     
  Lines       19738    19772      +34     
  Branches     2957     2958       +1     
==========================================
  Hits        16731    16731              
- Misses       3007     3041      +34     

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