Update Implementations for Caesar Cipher

[SpiderMath]

Description

This adds the links to JavaScript, C++, PHP implementations to Caesar cipher.

Checklist

• [x] A description of the changes in this PR is mentioned above.
• [x] All the new and existing checks pass.
• [x] No plagiarized, duplicated, or repetitive documentation that has been directly copied from another source.
• [ ] If it's a new explanation, it contains solid, understandable, and accessible information.
• [x] I have read the whole contributing guidelines and agree to the Code of Conduct.

Screenshots (if any)

Note to reviewers

[github-actions[bot]]

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