update CONTRIBUTING.md

[kan-ish]

Update CONTRIBUTING.md. Issue #328

Title : Fixed typos in CONTRIBUTING.md as per issue #328.

Issue No. : #328

Code Stack : Markdown

Close #328

Checklist:

• [X] I have mentioned the issue number in my Pull Request.
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have created a helpful and easy to understand README.md
• [X] I have updated the Index.html file for my contribution

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