chore(deps): update dependency gulp-mocha to v6 - autoclosed

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This PR contains the following updates:

Package	Type	Update	Change
gulp-mocha	devDependencies	major	^5.0.0 -> ^6.0.0

By merging this PR, the below issues will be automatically resolved and closed:

Severity	CVSS Score	CVE	GitHub Issue
High	7.5	WS-2021-0638	#62

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Release Notes

sindresorhus/gulp-mocha

### [`v6.0.0`](https://togithub.com/sindresorhus/gulp-mocha/compare/v5.0.0...v6.0.0) [Compare Source](https://togithub.com/sindresorhus/gulp-mocha/compare/v5.0.0...v6.0.0)

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• [ ] If you want to rebase/retry this PR, check this box

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⚠ Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this PR as-is.

♻ Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you click the rebase/retry checkbox if found above, or
• you rename this PR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: package-lock.json

/opt/buildpack/tools/npm/6.14.18/node_modules/npm/bin/npm-cli.js:87
      let notifier = require('update-notifier')({pkg})
      ^^^

SyntaxError: Block-scoped declarations (let, const, function, class) not yet supported outside strict mode
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:373:25)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Function.Module.runMain (module.js:441:10)
    at startup (node.js:139:18)
    at node.js:968:3