Update dependency eslint-plugin-unicorn to v20

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
eslint-plugin-unicorn	devDependencies	major	19.0.1 -> 20.0.0

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Release Notes

sindresorhus/eslint-plugin-unicorn

### [`v20.0.0`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/releases/v20.0.0) [Compare Source](https://togithub.com/sindresorhus/eslint-plugin-unicorn/compare/v19.0.1...v20.0.0) ##### Breaking - Require [ESLint 7](https://eslint.org/blog/2020/05/eslint-v7.0.0-released) ([#​577](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/577)) [`e4f44f3`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/e4f44f3) ##### New rules - Add [`prefer-optional-catch-binding`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/prefer-optional-catch-binding.md) rule ([#​671](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/671)) [`efdb03a`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/efdb03a) - Add [`no-useless-undefined`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/no-useless-undefined.md) rule ([#​718](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/718)) [`30dbe6d`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/30dbe6d) - Add [`no-reduce`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/no-reduce.md) rule ([#​704](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/704)) [`06ed7ee`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/06ed7ee) ##### Improvements - `throw-new-error`: Check `MemberExpression` customError ([#​716](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/716)) [`a28aad5`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/a28aad5) - `prefer-starts-ends-with`: Add auto-fix ([#​711](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/711)) [`da978e3`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/da978e3) - `consistent-function-scoping`: Ignore IIFE ([#​707](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/707)) [`1f4413d`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/1f4413d) - `prefer-set-has`: Ignore arrays only checking existence once ([#​706](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/706)) [`54c6f54`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/54c6f54) ##### Fixes - `prefer-starts-ends-with`: Fix bug with `m` flag ([#​721](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/721)) [`83bbabc`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/83bbabc) - `prefer-string-slice`: Handle negative length in `.substr()` ([#​709](https://togithub.com/sindresorhus/eslint-plugin-unicorn/issues/709)) [`7439465`](https://togithub.com/sindresorhus/eslint-plugin-unicorn/commit/7439465)

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