Update dependency eslint-config-prettier to v6.4.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
eslint-config-prettier	devDependencies	minor	6.3.0 -> 6.4.0

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Release Notes

prettier/eslint-config-prettier

### [`v6.4.0`](https://togithub.com/prettier/eslint-config-prettier/blob/master/CHANGELOG.md#Version-640-2019-10-05) [Compare Source](https://togithub.com/prettier/eslint-config-prettier/compare/v6.3.0...v6.4.0) - Added: [unicorn/no-nested-ternary]. Thanks to Yang Mingshan ([@​yangmingshan](https://togithub.com/yangmingshan))!

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