Update dependency gulp-mocha to v7

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
gulp-mocha	devDependencies	major	6.0.0 -> 7.0.2

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Release Notes

sindresorhus/gulp-mocha

### [`v7.0.2`](https://togithub.com/sindresorhus/gulp-mocha/releases/v7.0.2) [Compare Source](https://togithub.com/sindresorhus/gulp-mocha/compare/v7.0.1...v7.0.2) - Make Gulp an optional peer dependency [`8e452db`](https://togithub.com/sindresorhus/gulp-mocha/commit/8e452db) ### [`v7.0.1`](https://togithub.com/sindresorhus/gulp-mocha/releases/v7.0.1) [Compare Source](https://togithub.com/sindresorhus/gulp-mocha/compare/v7.0.0...v7.0.1) - Fix regressions in v7 ([#​197](https://togithub.com/sindresorhus/gulp-mocha/issues/197)) [`f60a346`](https://togithub.com/sindresorhus/gulp-mocha/commit/f60a346) ### [`v7.0.0`](https://togithub.com/sindresorhus/gulp-mocha/releases/v7.0.0) [Compare Source](https://togithub.com/sindresorhus/gulp-mocha/compare/v6.0.0...v7.0.0) Breaking: - Update Mocha ([release notes](https://togithub.com/mochajs/mocha/releases/tag/v6.0.0)) [`4924437`](https://togithub.com/sindresorhus/gulp-mocha/commit/4924437) - Require Node.js 8 and Gulp 4 [`4924437`](https://togithub.com/sindresorhus/gulp-mocha/commit/4924437)

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