Update mocha to version 2.5.2 🚀

[greenkeeperio-bot]

Hello :wave:

:rocket::rocket::rocket:

mocha just published its new version 2.5.2, which is not covered by your current version range.

If this pull request passes your tests you can publish your software with the latest version of mocha – otherwise use this branch to work on adaptions and fixes.

Happy fixing and merging :palm_tree:

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The new version differs by 5 commits .

• fdbbe40 Release v2.5.2
• c094f20 Rebuild mocha.js
• 7c134ea Update CHANGELOG.md for v2.5.2 [ci skip]
• 25f9378 Add .envrc to .gitignore
• 49b5ff1 Avoid double and triple xUnit XML escaping (#2178)

See the full diff.

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