docs: replace lingering Gitter links

[batpigandme]

Description

What is the purpose of this pull request?

This pull request: is a continuation of #8923 that includes files missed in my IDE search. Committed with --no-verify as warnings were unrelated to this PR, and I didn't want to change anything in the package publishing workflow (happy to make the edits if you think they're legit).

Questions

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No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

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• No

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• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
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{{TODO: add disclosure if applicable}}

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@stdlib-js/reviewers

[Planeshifter]

LGTM! And agreed it's better to keep the PR self-contained in this case and accept the lint error, which we can resolve in a follow-up later.

[stdlib-bot]

PR Commit Message

docs: replace lingering Gitter links

PR-URL: https://github.com/stdlib-js/stdlib/pull/9255
Ref: https://github.com/stdlib-js/stdlib/issues/8923

Reviewed-by: Philipp Burckhardt <pburckhardt@outlook.com>

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