Update dependency eslint-config-prettier to ^6.9.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
eslint-config-prettier	devDependencies	minor	^6.7.0 -> ^6.9.0

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Release Notes

prettier/eslint-config-prettier

### [`v6.9.0`](https://togithub.com/prettier/eslint-config-prettier/blob/master/CHANGELOG.md#Version-690-2019-12-27) [Compare Source](https://togithub.com/prettier/eslint-config-prettier/compare/v6.8.0...v6.9.0) - Added: [vue/max-len]. Thanks to [@​xcatliu](https://togithub.com/xcatliu)! ### [`v6.8.0`](https://togithub.com/prettier/eslint-config-prettier/blob/master/CHANGELOG.md#Version-680-2019-12-25) [Compare Source](https://togithub.com/prettier/eslint-config-prettier/compare/dcca556e260af985ece4d9af92531fa649268f80...v6.8.0) - Added: [@​typescript-eslint/no-extra-semi]. Thanks to [@​xcatliu](https://togithub.com/xcatliu)!

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