Update dependency load-grunt-tasks to v5

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
load-grunt-tasks	devDependencies	major	3.5.2 -> 5.0.0

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Release Notes

sindresorhus/load-grunt-tasks

### [`v5.0.0`](https://togithub.com/sindresorhus/load-grunt-tasks/releases/v5.0.0) [Compare Source](https://togithub.com/sindresorhus/load-grunt-tasks/compare/v4.0.0...v5.0.0) Breaking: - Require Node.js 8 [`a928bc7`](https://togithub.com/sindresorhus/load-grunt-tasks/commit/a928bc7) Enhancements: - Upgrade dependencies [`a928bc7`](https://togithub.com/sindresorhus/load-grunt-tasks/commit/a928bc7) ### [`v4.0.0`](https://togithub.com/sindresorhus/load-grunt-tasks/compare/v3.5.2...v4.0.0) [Compare Source](https://togithub.com/sindresorhus/load-grunt-tasks/compare/v3.5.2...v4.0.0)

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