docs: correct function description and indentation in math/base/assert/is-even

[gunjjoshi]

Description

What is the purpose of this pull request?

This pull request:

• corrects the function description in the C implementation in math/base/assert/is-even.
• replaces spaces by tabs in example.c and main.c.

Related Issues

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Checklist

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• Read, understood, and followed the contributing guidelines.

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@stdlib-js/reviewers

[stdlib-bot]

PR Commit Message

docs: correct function description and indentation in `math/base/assert/is-even`

PR-URL: https://github.com/stdlib-js/stdlib/pull/3078

Co-authored-by: 
Reviewed-by: Philipp Burckhardt <[email protected]>

Please review the above commit message and make any necessary adjustments.