Docs: Add missing double quote.

[eventualbuddha]

What is the purpose of this pull request? (put an "X" next to item)

[X] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

Please check each item to ensure your pull request is ready:

• I've read the pull request guide
• I've included tests for my change
• I've updated documentation for my change (if appropriate)

What changes did you make? (Give an overview)

I added a missing double quote in a string literal option.

Is there anything you'd like reviewers to focus on?

No.

[mention-bot]

@eventualbuddha, thanks for your PR! By analyzing the annotation information on this pull request, we identified @pedrottimark, @martijndeh and @lemonmade to be potential reviewers

[eslintbot]

LGTM

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[kaicataldo]

LGTM. Thanks for contributing to ESLint!