Include XO style guide in eslint --init

[fregante]

Prerequisites checklist

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

[ ] Documentation update
[ ] Bug fix (template)
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[x] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

XO is a pretty strict and popular ESLint config by Sindre Sorhus, I was surprised not to find it among the ones listed in eslint --init. It’s usually used through XO’s own CLI tool but this config works everywhere.

[eslint-github-bot]

Hi @fregante!, thanks for the Pull Request

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[nzakas]

LGTM