Update dependency grunt-concurrent to v3

[mend-for-github-com[bot]]

This PR contains the following updates:

Package	Type	Update	Change
grunt-concurrent	devDependencies	major	^2.3.0 -> ^3.0.0

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Release Notes

sindresorhus/grunt-concurrent

### [`v3.0.0`](https://togithub.com/sindresorhus/grunt-concurrent/releases/v3.0.0) [Compare Source](https://togithub.com/sindresorhus/grunt-concurrent/compare/v2.3.1...v3.0.0) Breaking: - Require Node.js 8 and Grunt 1 [`468aec3`](https://togithub.com/sindresorhus/grunt-concurrent/commit/468aec3) Enhancements: - Add `indent` option ([#​101](https://togithub.com/sindresorhus/grunt-concurrent/issues/101)) [`f8e1fd9`](https://togithub.com/sindresorhus/grunt-concurrent/commit/f8e1fd9)

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