build(deps-dev): update mocha requirement from ^5.1.1 to ^6.1.4

[dependabot-preview]

Updates the requirements on mocha to permit the latest version.

Release notes

Sourced from mocha's releases.

v6.1.4

6.1.4 / 2019-04-18

🔒 Security Fixes

• #3877: Upgrade js-yaml, addressing code injection vulnerability ([@​bjornstar](https://github.com/bjornstar))

Changelog

Sourced from mocha's changelog.

6.1.4 / 2019-04-18

🔒 Security Fixes

• #3877: Upgrade js-yaml, addressing code injection vulnerability ([@​bjornstar](https://github.com/bjornstar))

6.1.3 / 2019-04-11

🐛 Fixes

• #3863: Fix yargs-related global scope pollution ([@​inukshuk](https://github.com/inukshuk))
• #3869: Fix failure when installed w/ pnpm ([@​boneskull](https://github.com/boneskull))

6.1.2 / 2019-04-08

🐛 Fixes

• #3867: Re-publish v6.1.1 from POSIX OS to avoid dropped executable flags ([@​boneskull](https://github.com/boneskull))

6.1.1 / 2019-04-07

🐛 Fixes

• #3866: Fix Windows End-of-Line publishing issue ([@​juergba](https://github.com/juergba) & [@​cspotcode](https://github.com/cspotcode))

6.1.0 / 2019-04-07

🔒 Security Fixes

• #3845: Update dependency "js-yaml" to v3.13.0 per npm security advisory ([@​plroebuck](https://github.com/plroebuck))

🎉 Enhancements

• #3766: Make reporter constructor support optional options parameter ([@​plroebuck](https://github.com/plroebuck))
• #3760: Add support for config files with .jsonc extension ([@​sstephant](https://github.com/sstephant))

📠 Deprecations

These are soft-deprecated, and will emit a warning upon use. Support will be removed in (likely) the next major version of Mocha:

• #3719: Deprecate this.skip() for "after all" hooks ([@​juergba](https://github.com/juergba))

🐛 Fixes

• #3829: Use cwd-relative pathname to load config file ([@​plroebuck](https://github.com/plroebuck))
• #3745: Fix async calls of this.skip() in "before each" hooks ([@​juergba](https://github.com/juergba))
• #3669: Enable --allow-uncaught for uncaught exceptions thrown inside hooks ([@​givanse](https://github.com/givanse))

and some regressions:

... (truncated)

Commits

• 31c019e Release v6.1.4
• c3d241e update CHANGELOG.md for v6.1.4 [ci skip]
• 0d9d4a3 Update js-yaml from 3.13.0 to 3.13.1 (#3877)
• f1fe632 Release v6.1.3
• ae3d53f update CHANGELOG for v6.1.3 [ci skip]
• e73941a upgrade node-environment-flags; closes #3868
• 5121211 Do not pass argv twice
• f05a58f Fix yargs global pollution
• 86cd699 Release v6.1.2
• 2e8f31f update CHANGELOG for v6.1.2
• Additional commits viewable in compare view

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[coveralls]

Pull Request Test Coverage Report for Build 641

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.875%

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Totals
Change from base Build 638:	0.0%
Covered Lines:	574
Relevant Lines:	579

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💛 - Coveralls

[dependabot-preview]

Superseded by #116.