Update dependency grunt-eslint to v23

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
grunt-eslint	devDependencies	major	^20.1.0 -> ^23.0.0

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Release Notes

sindresorhus/grunt-eslint

### [`v23.0.0`](https://togithub.com/sindresorhus/grunt-eslint/releases/v23.0.0) [Compare Source](https://togithub.com/sindresorhus/grunt-eslint/compare/v22.0.0...v23.0.0) ##### Breaking - Upgrade to ESLint 7 ([#​167](https://togithub.com/sindresorhus/grunt-eslint/issues/167)) [`a8f45f6`](https://togithub.com/sindresorhus/grunt-eslint/commit/a8f45f6) - Require Node.js 10 ([#​167](https://togithub.com/sindresorhus/grunt-eslint/issues/167)) [`a8f45f6`](https://togithub.com/sindresorhus/grunt-eslint/commit/a8f45f6) ### [`v22.0.0`](https://togithub.com/sindresorhus/grunt-eslint/releases/v22.0.0) [Compare Source](https://togithub.com/sindresorhus/grunt-eslint/compare/v21.1.0...v22.0.0) Breaking: - Upgrade to [ESLint 6](https://eslint.org/blog/2019/06/eslint-v6.0.0-released) [`7707f60`](https://togithub.com/sindresorhus/grunt-eslint/commit/7707f60) - Require Node.js 8 [`7707f60`](https://togithub.com/sindresorhus/grunt-eslint/commit/7707f60) ### [`v21.1.0`](https://togithub.com/sindresorhus/grunt-eslint/releases/v21.1.0) [Compare Source](https://togithub.com/sindresorhus/grunt-eslint/compare/v21.0.0...v21.1.0) - Bump the eslint version to 5.16.0 ([#​161](https://togithub.com/sindresorhus/grunt-eslint/issues/161)) [`7950891`](https://togithub.com/sindresorhus/grunt-eslint/commit/7950891) ### [`v21.0.0`](https://togithub.com/sindresorhus/grunt-eslint/compare/v20.2.0...v21.0.0) [Compare Source](https://togithub.com/sindresorhus/grunt-eslint/compare/v20.2.0...v21.0.0)

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